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 $83.86   11.317%   $93.3504   $93.35   $93.35   $93.40  
  Purchase #2 $91.43   6.575%   $97.4415   $97.44   $97.45   $97.40  
  Purchase #3 $218.91   7.384%   $235.0743   $235.07   $235.05   $235.10  
  Purchase #4 $90.55   3.347%   $93.5807   $93.58   $93.60   $93.60  
  Purchase #5 $85.73   11.351%   $95.4612   $95.46   $95.45   $95.50  
  Purchase #6 $113.68   10.306%   $125.3959   $125.40   $125.40   $125.40  
  Purchase #7 $58.27   13.482%   $66.126   $66.13   $66.15   $66.10  
  7 purchase totals = $742.43       $806.4300   $806.43   $806.45   $806.50