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 $176.80   9.311%   $193.2618   $193.26   $193.25   $193.30  
  Purchase #2 $36.54   12.465%   $41.0947   $41.09   $41.10   $41.10  
  Purchase #3 $44.34   12.331%   $49.8076   $49.81   $49.80   $49.80  
  Purchase #4 $54.44   8.266%   $58.94   $58.94   $58.95   $58.90  
  Purchase #5 $68.85   10.259%   $75.9133   $75.91   $75.90   $75.90  
  Purchase #6 $229.96   13.295%   $260.5332   $260.53   $260.55   $260.50  
  Purchase #7 $164.94   4.114%   $171.7256   $171.73   $171.75   $171.70  
  7 purchase totals = $775.87       $851.2762   $851.27   $851.30   $851.20