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 $232.89   8.775%   $253.3261   $253.33   $253.35   $253.30  
  Purchase #2 $153.39   8.542%   $166.4926   $166.49   $166.50   $166.50  
  Purchase #3 $127.84   11.552%   $142.6081   $142.61   $142.60   $142.60  
  Purchase #4 $44.34   7.593%   $47.7067   $47.71   $47.70   $47.70  
  Purchase #5 $241.25   11.780%   $269.6693   $269.67   $269.65   $269.70  
  Purchase #6 $170.90   6.502%   $182.0119   $182.01   $182.00   $182.00  
  Purchase #7 $185.29   12.338%   $208.1511   $208.15   $208.15   $208.20  
  7 purchase totals = $1,155.90       $1,269.9658   $1,269.97   $1,269.95   $1,270.00