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 $176.35   5.336%   $185.76   $185.76   $185.75   $185.80  
  Purchase #2 $61.63   7.443%   $66.2171   $66.22   $66.20   $66.20  
  Purchase #3 $104.72   8.623%   $113.75   $113.75   $113.75   $113.80  
  Purchase #4 $232.97   6.403%   $247.8871   $247.89   $247.90   $247.90  
  Purchase #5 $36.25   9.622%   $39.738   $39.74   $39.75   $39.70  
  Purchase #6 $173.61   9.497%   $190.0977   $190.10   $190.10   $190.10  
  Purchase #7 $101.41   10.846%   $112.4089   $112.41   $112.40   $112.40  
  7 purchase totals = $886.94       $955.8588   $955.87   $955.85   $955.90