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 $28.83   13.265%   $32.6543   $32.65   $32.65   $32.70  
  Purchase #2 $58.90   9.281%   $64.3665   $64.37   $64.35   $64.40  
  Purchase #3 $116.73   9.594%   $127.9291   $127.93   $127.95   $127.90  
  Purchase #4 $165.98   5.404%   $174.9496   $174.95   $174.95   $174.90  
  Purchase #5 $207.66   6.802%   $221.785   $221.79   $221.80   $221.80  
  Purchase #6 $117.82   12.520%   $132.5711   $132.57   $132.55   $132.60  
  Purchase #7 $173.40   4.504%   $181.2099   $181.21   $181.20   $181.20  
  7 purchase totals = $869.32       $935.4655   $935.47   $935.45   $935.50