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 $86.75   6.662%   $92.5293   $92.53   $92.55   $92.50  
  Purchase #2 $98.78   7.283%   $105.9741   $105.97   $105.95   $106.00  
  Purchase #3 $131.98   3.658%   $136.8078   $136.81   $136.80   $136.80  
  Purchase #4 $154.88   3.347%   $160.0638   $160.06   $160.05   $160.10  
  Purchase #5 $102.31   4.549%   $106.9641   $106.96   $106.95   $107.00  
  Purchase #6 $233.43   11.696%   $260.732   $260.73   $260.75   $260.70  
  Purchase #7 $9.55   10.536%   $10.5562   $10.56   $10.55   $10.60  
  7 purchase totals = $817.68       $873.6273   $873.62   $873.60   $873.70