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 $221.93   10.174%   $244.5092   $244.51   $244.50   $244.50  
  Purchase #2 $103.64   13.507%   $117.6387   $117.64   $117.65   $117.60  
  Purchase #3 $91.29   9.549%   $100.0073   $100.01   $100.00   $100.00  
  Purchase #4 $14.84   9.180%   $16.2023   $16.20   $16.20   $16.20  
  Purchase #5 $189.79   10.109%   $208.9759   $208.98   $209.00   $209.00  
  Purchase #6 $148.67   5.691%   $157.1308   $157.13   $157.15   $157.10  
  Purchase #7 $20.93   12.314%   $23.5073   $23.51   $23.50   $23.50  
  7 purchase totals = $791.09       $867.9715   $867.98   $868.00   $867.90