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 $80.46   8.283%   $87.1245   $87.12   $87.10   $87.10  
  Purchase #2 $147.57   4.239%   $153.8255   $153.83   $153.85   $153.80  
  Purchase #3 $153.50   8.173%   $166.0456   $166.05   $166.05   $166.00  
  Purchase #4 $178.95   6.714%   $190.9647   $190.96   $190.95   $191.00  
  Purchase #5 $239.54   5.150%   $251.8763   $251.88   $251.90   $251.90  
  Purchase #6 $173.47   4.704%   $181.63   $181.63   $181.65   $181.60  
  Purchase #7 $215.31   11.344%   $239.7348   $239.73   $239.75   $239.70  
  7 purchase totals = $1,188.80       $1,271.2014   $1,271.20   $1,271.25   $1,271.10