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 $176.79   10.763%   $195.8179   $195.82   $195.80   $195.80  
  Purchase #2 $154.92   12.598%   $174.4368   $174.44   $174.45   $174.40  
  Purchase #3 $55.50   8.464%   $60.1975   $60.20   $60.20   $60.20  
  Purchase #4 $114.93   5.278%   $120.996   $121.00   $121.00   $121.00  
  Purchase #5 $47.88   12.833%   $54.0244   $54.02   $54.00   $54.00  
  Purchase #6 $92.26   10.531%   $101.9759   $101.98   $102.00   $102.00  
  Purchase #7 $130.79   4.505%   $136.6821   $136.68   $136.70   $136.70  
  7 purchase totals = $773.07       $844.1306   $844.14   $844.15   $844.10