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 $210.62   11.871%   $235.6227   $235.62   $235.60   $235.60  
  Purchase #2 $199.76   13.769%   $227.265   $227.27   $227.25   $227.30  
  Purchase #3 $115.47   5.477%   $121.7943   $121.79   $121.80   $121.80  
  Purchase #4 $241.34   5.718%   $255.1398   $255.14   $255.15   $255.10  
  Purchase #5 $226.76   10.463%   $250.4859   $250.49   $250.50   $250.50  
  Purchase #6 $89.46   6.746%   $95.495   $95.50   $95.50   $95.50  
  Purchase #7 $140.97   6.299%   $149.8497   $149.85   $149.85   $149.80  
  7 purchase totals = $1,224.38       $1,335.6524   $1,335.66   $1,335.65   $1,335.60