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 $48.35   13.662%   $54.9556   $54.96   $54.95   $55.00  
  Purchase #2 $118.46   11.813%   $132.4537   $132.45   $132.45   $132.50  
  Purchase #3 $214.60   10.749%   $237.6674   $237.67   $237.65   $237.70  
  Purchase #4 $131.93   5.626%   $139.3524   $139.35   $139.35   $139.40  
  Purchase #5 $60.55   3.759%   $62.8261   $62.83   $62.85   $62.80  
  Purchase #6 $195.25   11.150%   $217.0204   $217.02   $217.00   $217.00  
  Purchase #7 $126.28   4.570%   $132.051   $132.05   $132.05   $132.10  
  7 purchase totals = $895.42       $976.3266   $976.33   $976.30   $976.50