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 $83.46   12.746%   $94.0978   $94.10   $94.10   $94.10  
  Purchase #2 $202.30   7.286%   $217.0396   $217.04   $217.05   $217.00  
  Purchase #3 $124.38   3.790%   $129.094   $129.09   $129.10   $129.10  
  Purchase #4 $95.69   3.481%   $99.021   $99.02   $99.00   $99.00  
  Purchase #5 $31.82   8.788%   $34.6163   $34.62   $34.60   $34.60  
  Purchase #6 $98.97   6.779%   $105.6792   $105.68   $105.70   $105.70  
  Purchase #7 $233.69   11.677%   $260.978   $260.98   $261.00   $261.00  
  7 purchase totals = $870.31       $940.5259   $940.53   $940.55   $940.50