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 $61.89   12.872%   $69.8565   $69.86   $69.85   $69.90  
  Purchase #2 $217.37   8.603%   $236.0703   $236.07   $236.05   $236.10  
  Purchase #3 $104.87   6.565%   $111.7547   $111.75   $111.75   $111.80  
  Purchase #4 $215.92   7.583%   $232.2932   $232.29   $232.30   $232.30  
  Purchase #5 $60.27   10.486%   $66.5899   $66.59   $66.60   $66.60  
  Purchase #6 $50.89   13.757%   $57.8909   $57.89   $57.90   $57.90  
  Purchase #7 $165.63   8.263%   $179.316   $179.32   $179.30   $179.30  
  7 purchase totals = $876.84       $953.7715   $953.77   $953.75   $953.90