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 $211.61   6.797%   $225.9931   $225.99   $226.00   $226.00  
  Purchase #2 $80.44   6.853%   $85.9526   $85.95   $85.95   $86.00  
  Purchase #3 $210.38   8.407%   $228.0666   $228.07   $228.05   $228.10  
  Purchase #4 $17.98   7.236%   $19.281   $19.28   $19.30   $19.30  
  Purchase #5 $56.76   3.212%   $58.5831   $58.58   $58.60   $58.60  
  Purchase #6 $111.30   3.502%   $115.1977   $115.20   $115.20   $115.20  
  Purchase #7 $218.40   8.316%   $236.5621   $236.56   $236.55   $236.60  
  7 purchase totals = $906.87       $969.6362   $969.63   $969.65   $969.80