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 $86.66   10.129%   $95.4378   $95.44   $95.45   $95.40  
  Purchase #2 $141.32   12.194%   $158.5526   $158.55   $158.55   $158.60  
  Purchase #3 $106.81   12.269%   $119.9145   $119.91   $119.90   $119.90  
  Purchase #4 $33.90   7.371%   $36.3988   $36.40   $36.40   $36.40  
  Purchase #5 $139.79   12.257%   $156.9241   $156.92   $156.90   $156.90  
  Purchase #6 $59.35   8.380%   $64.3235   $64.32   $64.30   $64.30  
  Purchase #7 $195.81   7.469%   $210.435   $210.44   $210.45   $210.40  
  7 purchase totals = $763.64       $841.9863   $841.98   $841.95   $841.90