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 $82.86   11.237%   $92.171   $92.17   $92.15   $92.20  
  Purchase #2 $183.69   6.413%   $195.47   $195.47   $195.45   $195.50  
  Purchase #3 $19.44   11.787%   $21.7314   $21.73   $21.75   $21.70  
  Purchase #4 $56.72   11.434%   $63.2054   $63.21   $63.20   $63.20  
  Purchase #5 $240.56   4.569%   $251.5512   $251.55   $251.55   $251.60  
  Purchase #6 $66.99   13.178%   $75.8179   $75.82   $75.80   $75.80  
  Purchase #7 $85.98   8.206%   $93.0355   $93.04   $93.05   $93.00  
  7 purchase totals = $736.24       $792.9824   $792.99   $792.95   $793.00