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 $84.71   9.419%   $92.6888   $92.69   $92.70   $92.70  
  Purchase #2 $119.31   11.193%   $132.6644   $132.66   $132.65   $132.70  
  Purchase #3 $59.70   10.727%   $66.104   $66.10   $66.10   $66.10  
  Purchase #4 $70.91   6.726%   $75.6794   $75.68   $75.70   $75.70  
  Purchase #5 $153.33   6.174%   $162.7966   $162.80   $162.80   $162.80  
  Purchase #6 $225.51   4.569%   $235.8136   $235.81   $235.80   $235.80  
  Purchase #7 $96.53   7.460%   $103.7311   $103.73   $103.75   $103.70  
  7 purchase totals = $810.00       $869.4779   $869.47   $869.50   $869.50