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 $179.87   7.473%   $193.3117   $193.31   $193.30   $193.30  
  Purchase #2 $146.25   11.202%   $162.6329   $162.63   $162.65   $162.60  
  Purchase #3 $219.56   13.780%   $249.8154   $249.82   $249.80   $249.80  
  Purchase #4 $156.78   13.119%   $177.348   $177.35   $177.35   $177.30  
  Purchase #5 $228.94   12.755%   $258.1413   $258.14   $258.15   $258.10  
  Purchase #6 $240.43   10.431%   $265.5093   $265.51   $265.50   $265.50  
  Purchase #7 $176.95   4.709%   $185.2826   $185.28   $185.30   $185.30  
  7 purchase totals = $1,348.78       $1,492.0412   $1,492.04   $1,492.05   $1,491.90