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 $68.81   6.787%   $73.4801   $73.48   $73.50   $73.50  
  Purchase #2 $188.53   3.143%   $194.4555   $194.46   $194.45   $194.50  
  Purchase #3 $64.62   5.282%   $68.0332   $68.03   $68.05   $68.00  
  Purchase #4 $60.70   12.651%   $68.3792   $68.38   $68.40   $68.40  
  Purchase #5 $128.49   13.288%   $145.5638   $145.56   $145.55   $145.60  
  Purchase #6 $248.34   7.591%   $267.1915   $267.19   $267.20   $267.20  
  Purchase #7 $177.30   12.334%   $199.1682   $199.17   $199.15   $199.20  
  7 purchase totals = $936.79       $1,016.2715   $1,016.27   $1,016.30   $1,016.40