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 $58.51   8.107%   $63.2534   $63.25   $63.25   $63.30  
  Purchase #2 $179.54   8.291%   $194.4257   $194.43   $194.45   $194.40  
  Purchase #3 $218.97   7.790%   $236.0278   $236.03   $236.05   $236.00  
  Purchase #4 $46.96   8.306%   $50.8605   $50.86   $50.85   $50.90  
  Purchase #5 $30.56   8.275%   $33.0888   $33.09   $33.10   $33.10  
  Purchase #6 $152.62   13.402%   $173.0741   $173.07   $173.05   $173.10  
  Purchase #7 $124.97   3.389%   $129.2052   $129.21   $129.20   $129.20  
  7 purchase totals = $812.13       $879.9355   $879.94   $879.95   $880.00