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 $58.87   8.269%   $63.738   $63.74   $63.75   $63.70  
  Purchase #2 $179.87   11.618%   $200.7673   $200.77   $200.75   $200.80  
  Purchase #3 $197.53   9.228%   $215.7581   $215.76   $215.75   $215.80  
  Purchase #4 $42.84   7.458%   $46.035   $46.04   $46.05   $46.00  
  Purchase #5 $108.97   9.426%   $119.2415   $119.24   $119.25   $119.20  
  Purchase #6 $88.51   7.477%   $95.1279   $95.13   $95.15   $95.10  
  Purchase #7 $49.97   5.733%   $52.8348   $52.83   $52.85   $52.80  
  7 purchase totals = $726.56       $793.5026   $793.51   $793.55   $793.40