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 $174.90   12.697%   $197.1071   $197.11   $197.10   $197.10  
  Purchase #2 $104.79   11.518%   $116.8597   $116.86   $116.85   $116.90  
  Purchase #3 $225.65   4.798%   $236.4767   $236.48   $236.50   $236.50  
  Purchase #4 $49.39   12.167%   $55.3993   $55.40   $55.40   $55.40  
  Purchase #5 $81.56   4.200%   $84.9855   $84.99   $85.00   $85.00  
  Purchase #6 $59.64   8.544%   $64.7356   $64.74   $64.75   $64.70  
  Purchase #7 $69.90   4.136%   $72.7911   $72.79   $72.80   $72.80  
  7 purchase totals = $765.83       $828.3550   $828.37   $828.40   $828.40