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 $80.89   7.154%   $86.6769   $86.68   $86.70   $86.70  
  Purchase #2 $144.96   10.480%   $160.1518   $160.15   $160.15   $160.20  
  Purchase #3 $215.93   4.656%   $225.9837   $225.98   $226.00   $226.00  
  Purchase #4 $68.83   7.855%   $74.2366   $74.24   $74.25   $74.20  
  Purchase #5 $29.68   10.495%   $32.7949   $32.79   $32.80   $32.80  
  Purchase #6 $110.44   5.556%   $116.576   $116.58   $116.60   $116.60  
  Purchase #7 $220.46   11.282%   $245.3323   $245.33   $245.35   $245.30  
  7 purchase totals = $871.19       $941.7522   $941.75   $941.85   $941.80