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 $213.66   12.686%   $240.7649   $240.76   $240.75   $240.80  
  Purchase #2 $95.89   13.618%   $108.9483   $108.95   $108.95   $108.90  
  Purchase #3 $64.37   7.146%   $68.9699   $68.97   $68.95   $69.00  
  Purchase #4 $250.41   7.319%   $268.7375   $268.74   $268.75   $268.70  
  Purchase #5 $11.51   4.600%   $12.0395   $12.04   $12.05   $12.00  
  Purchase #6 $239.37   7.184%   $256.5663   $256.57   $256.55   $256.60  
  Purchase #7 $59.95   4.140%   $62.4319   $62.43   $62.45   $62.40  
  7 purchase totals = $935.16       $1,018.4583   $1,018.46   $1,018.45   $1,018.40