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 $70.74   8.139%   $76.4975   $76.50   $76.50   $76.50  
  Purchase #2 $216.54   6.512%   $230.6411   $230.64   $230.65   $230.60  
  Purchase #3 $93.97   4.715%   $98.4007   $98.40   $98.40   $98.40  
  Purchase #4 $89.39   4.568%   $93.4733   $93.47   $93.45   $93.50  
  Purchase #5 $23.39   10.637%   $25.878   $25.88   $25.90   $25.90  
  Purchase #6 $164.83   5.283%   $173.538   $173.54   $173.55   $173.50  
  Purchase #7 $87.89   10.547%   $97.1598   $97.16   $97.15   $97.20  
  7 purchase totals = $746.75       $795.5884   $795.59   $795.60   $795.60