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 $112.62   7.616%   $121.1971   $121.20   $121.20   $121.20  
  Purchase #2 $69.86   13.475%   $79.2736   $79.27   $79.25   $79.30  
  Purchase #3 $61.62   8.517%   $66.8682   $66.87   $66.85   $66.90  
  Purchase #4 $241.28   11.554%   $269.1575   $269.16   $269.15   $269.20  
  Purchase #5 $7.84   8.540%   $8.5095   $8.51   $8.50   $8.50  
  Purchase #6 $76.85   9.758%   $84.349   $84.35   $84.35   $84.30  
  Purchase #7 $100.32   10.412%   $110.7653   $110.77   $110.75   $110.80  
  7 purchase totals = $670.39       $740.1202   $740.13   $740.05   $740.20