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 $22.98   8.687%   $24.9763   $24.98   $25.00   $25.00  
  Purchase #2 $21.71   9.548%   $23.7829   $23.78   $23.80   $23.80  
  Purchase #3 $12.42   4.763%   $13.0116   $13.01   $13.00   $13.00  
  Purchase #4 $172.26   8.140%   $186.282   $186.28   $186.30   $186.30  
  Purchase #5 $69.85   6.428%   $74.34   $74.34   $74.35   $74.30  
  Purchase #6 $48.70   3.542%   $50.425   $50.43   $50.45   $50.40  
  Purchase #7 $211.60   5.283%   $222.7788   $222.78   $222.80   $222.80  
  7 purchase totals = $559.52       $595.5966   $595.60   $595.70   $595.60