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 $164.82   10.871%   $182.7376   $182.74   $182.75   $182.70  
  Purchase #2 $128.60   9.290%   $140.5469   $140.55   $140.55   $140.50  
  Purchase #3 $198.72   8.678%   $215.9649   $215.96   $215.95   $216.00  
  Purchase #4 $61.43   10.293%   $67.753   $67.75   $67.75   $67.80  
  Purchase #5 $236.50   7.676%   $254.6537   $254.65   $254.65   $254.70  
  Purchase #6 $43.55   13.313%   $49.3478   $49.35   $49.35   $49.30  
  Purchase #7 $23.80   7.692%   $25.6307   $25.63   $25.65   $25.60  
  7 purchase totals = $857.42       $936.6346   $936.63   $936.65   $936.60