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 $202.57   7.148%   $217.0497   $217.05   $217.05   $217.00  
  Purchase #2 $215.75   9.541%   $236.3347   $236.33   $236.35   $236.30  
  Purchase #3 $122.71   6.126%   $130.2272   $130.23   $130.25   $130.20  
  Purchase #4 $201.63   4.479%   $210.661   $210.66   $210.65   $210.70  
  Purchase #5 $85.39   8.414%   $92.5747   $92.57   $92.55   $92.60  
  Purchase #6 $149.47   8.642%   $162.3872   $162.39   $162.40   $162.40  
  Purchase #7 $120.38   4.792%   $126.1486   $126.15   $126.15   $126.10  
  7 purchase totals = $1,097.90       $1,175.3831   $1,175.38   $1,175.40   $1,175.30