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 $48.26   11.346%   $53.7356   $53.74   $53.75   $53.70  
  Purchase #2 $171.72   6.548%   $182.9642   $182.96   $182.95   $183.00  
  Purchase #3 $33.72   11.532%   $37.6086   $37.61   $37.60   $37.60  
  Purchase #4 $110.49   5.348%   $116.399   $116.40   $116.40   $116.40  
  Purchase #5 $168.98   10.240%   $186.2836   $186.28   $186.30   $186.30  
  Purchase #6 $197.48   6.138%   $209.6013   $209.60   $209.60   $209.60  
  Purchase #7 $113.39   3.589%   $117.4596   $117.46   $117.45   $117.50  
  7 purchase totals = $844.04       $904.0519   $904.05   $904.05   $904.10