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 $132.48   13.601%   $150.4986   $150.50   $150.50   $150.50  
  Purchase #2 $22.84   13.807%   $25.9935   $25.99   $26.00   $26.00  
  Purchase #3 $93.53   11.862%   $104.6245   $104.62   $104.60   $104.60  
  Purchase #4 $247.31   12.400%   $277.9764   $277.98   $278.00   $278.00  
  Purchase #5 $136.55   6.158%   $144.9587   $144.96   $144.95   $145.00  
  Purchase #6 $82.68   12.503%   $93.0175   $93.02   $93.00   $93.00  
  Purchase #7 $161.63   3.763%   $167.7121   $167.71   $167.70   $167.70  
  7 purchase totals = $877.02       $964.7813   $964.78   $964.75   $964.80