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 $59.87   11.797%   $66.9329   $66.93   $66.95   $66.90  
  Purchase #2 $212.42   7.337%   $228.0053   $228.01   $228.00   $228.00  
  Purchase #3 $25.94   12.209%   $29.107   $29.11   $29.10   $29.10  
  Purchase #4 $28.78   12.105%   $32.2638   $32.26   $32.25   $32.30  
  Purchase #5 $224.78   11.812%   $251.331   $251.33   $251.35   $251.30  
  Purchase #6 $103.67   11.481%   $115.5724   $115.57   $115.55   $115.60  
  Purchase #7 $225.34   3.391%   $232.9813   $232.98   $233.00   $233.00  
  7 purchase totals = $880.80       $956.1937   $956.19   $956.20   $956.20