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 $248.99   13.465%   $282.5165   $282.52   $282.50   $282.50  
  Purchase #2 $127.33   3.117%   $131.2989   $131.30   $131.30   $131.30  
  Purchase #3 $96.94   5.328%   $102.105   $102.11   $102.10   $102.10  
  Purchase #4 $88.63   3.496%   $91.7285   $91.73   $91.75   $91.70  
  Purchase #5 $66.97   7.476%   $71.9767   $71.98   $72.00   $72.00  
  Purchase #6 $213.62   4.569%   $223.3803   $223.38   $223.40   $223.40  
  Purchase #7 $20.95   13.706%   $23.8214   $23.82   $23.80   $23.80  
  7 purchase totals = $863.43       $926.8273   $926.84   $926.85   $926.80