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 $54.82   11.706%   $61.2372   $61.24   $61.25   $61.20  
  Purchase #2 $200.79   11.838%   $224.5595   $224.56   $224.55   $224.60  
  Purchase #3 $19.44   7.424%   $20.8832   $20.88   $20.90   $20.90  
  Purchase #4 $30.52   5.790%   $32.2871   $32.29   $32.30   $32.30  
  Purchase #5 $125.65   5.499%   $132.5595   $132.56   $132.55   $132.60  
  Purchase #6 $186.88   7.482%   $200.8624   $200.86   $200.85   $200.90  
  Purchase #7 $122.80   8.791%   $133.5953   $133.60   $133.60   $133.60  
  7 purchase totals = $740.90       $805.9842   $805.99   $806.00   $806.10