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 $76.89   11.807%   $85.9684   $85.97   $85.95   $86.00  
  Purchase #2 $59.66   9.685%   $65.4381   $65.44   $65.45   $65.40  
  Purchase #3 $158.39   8.163%   $171.3194   $171.32   $171.30   $171.30  
  Purchase #4 $92.75   12.647%   $104.4801   $104.48   $104.50   $104.50  
  Purchase #5 $26.97   12.251%   $30.2741   $30.27   $30.25   $30.30  
  Purchase #6 $193.63   6.460%   $206.1385   $206.14   $206.15   $206.10  
  Purchase #7 $197.59   12.433%   $222.1564   $222.16   $222.15   $222.20  
  7 purchase totals = $805.88       $885.7750   $885.78   $885.75   $885.80