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 $208.95   13.187%   $236.5042   $236.50   $236.50   $236.50  
  Purchase #2 $162.49   7.209%   $174.2039   $174.20   $174.20   $174.20  
  Purchase #3 $88.44   8.419%   $95.8858   $95.89   $95.90   $95.90  
  Purchase #4 $182.50   6.627%   $194.5943   $194.59   $194.60   $194.60  
  Purchase #5 $158.75   9.812%   $174.3266   $174.33   $174.35   $174.30  
  Purchase #6 $151.74   13.171%   $171.7257   $171.73   $171.75   $171.70  
  Purchase #7 $234.26   12.359%   $263.2122   $263.21   $263.20   $263.20  
  7 purchase totals = $1,187.13       $1,310.4527   $1,310.45   $1,310.50   $1,310.40