Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $244.92   10.861%   $271.5208   $271.52   $271.50   $271.50  
  Purchase #2 $153.56   13.110%   $173.6917   $173.69   $173.70   $173.70  
  Purchase #3 $137.30   10.119%   $151.1934   $151.19   $151.20   $151.20  
  Purchase #4 $231.84   13.260%   $262.582   $262.58   $262.60   $262.60  
  Purchase #5 $207.30   7.556%   $222.9636   $222.96   $222.95   $223.00  
  Purchase #6 $182.73   5.495%   $192.771   $192.77   $192.75   $192.80  
  Purchase #7 $233.33   11.797%   $260.8559   $260.86   $260.85   $260.90  
  7 purchase totals = $1,390.98       $1,535.5784   $1,535.57   $1,535.55   $1,535.70