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 $219.83   11.230%   $244.5169   $244.52   $244.50   $244.50  
  Purchase #2 $117.86   3.690%   $122.209   $122.21   $122.20   $122.20  
  Purchase #3 $159.75   9.285%   $174.5828   $174.58   $174.60   $174.60  
  Purchase #4 $121.93   10.415%   $134.629   $134.63   $134.65   $134.60  
  Purchase #5 $105.91   12.762%   $119.4262   $119.43   $119.45   $119.40  
  Purchase #6 $125.59   5.435%   $132.4158   $132.42   $132.40   $132.40  
  Purchase #7 $77.55   12.691%   $87.3919   $87.39   $87.40   $87.40  
  7 purchase totals = $928.42       $1,015.1716   $1,015.18   $1,015.20   $1,015.10