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 $214.68   6.265%   $228.1297   $228.13   $228.15   $228.10  
  Purchase #2 $169.81   7.528%   $182.5933   $182.59   $182.60   $182.60  
  Purchase #3 $59.89   7.359%   $64.2973   $64.30   $64.30   $64.30  
  Purchase #4 $199.93   3.819%   $207.5653   $207.57   $207.55   $207.60  
  Purchase #5 $60.50   5.817%   $64.0193   $64.02   $64.00   $64.00  
  Purchase #6 $85.85   13.856%   $97.7454   $97.75   $97.75   $97.70  
  Purchase #7 $232.39   6.496%   $247.4861   $247.49   $247.50   $247.50  
  7 purchase totals = $1,023.05       $1,091.8364   $1,091.85   $1,091.85   $1,091.80