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 $24.38   5.842%   $25.8043   $25.80   $25.80   $25.80  
  Purchase #2 $221.78   7.614%   $238.6663   $238.67   $238.65   $238.70  
  Purchase #3 $51.95   8.361%   $56.2935   $56.29   $56.30   $56.30  
  Purchase #4 $44.70   8.482%   $48.4915   $48.49   $48.50   $48.50  
  Purchase #5 $77.84   10.650%   $86.13   $86.13   $86.15   $86.10  
  Purchase #6 $161.63   9.306%   $176.6713   $176.67   $176.65   $176.70  
  Purchase #7 $108.41   8.844%   $117.9978   $118.00   $118.00   $118.00  
  7 purchase totals = $690.69       $750.0547   $750.05   $750.05   $750.10