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 $50.95   9.579%   $55.8305   $55.83   $55.85   $55.80  
  Purchase #2 $202.96   3.165%   $209.3837   $209.38   $209.40   $209.40  
  Purchase #3 $218.96   8.196%   $236.906   $236.91   $236.90   $236.90  
  Purchase #4 $189.67   5.153%   $199.4437   $199.44   $199.45   $199.40  
  Purchase #5 $83.56   6.355%   $88.8702   $88.87   $88.85   $88.90  
  Purchase #6 $96.74   8.803%   $105.256   $105.26   $105.25   $105.30  
  Purchase #7 $93.75   6.243%   $99.6028   $99.60   $99.60   $99.60  
  7 purchase totals = $936.59       $995.2929   $995.29   $995.30   $995.30