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 $224.47   9.737%   $246.3266   $246.33   $246.35   $246.30  
  Purchase #2 $89.32   6.527%   $95.1499   $95.15   $95.15   $95.10  
  Purchase #3 $60.61   4.578%   $63.3847   $63.38   $63.40   $63.40  
  Purchase #4 $179.62   7.393%   $192.8993   $192.90   $192.90   $192.90  
  Purchase #5 $218.57   4.857%   $229.1859   $229.19   $229.20   $229.20  
  Purchase #6 $28.26   3.347%   $29.2059   $29.21   $29.20   $29.20  
  Purchase #7 $162.84   10.567%   $180.0473   $180.05   $180.05   $180.00  
  7 purchase totals = $963.69       $1,036.1996   $1,036.21   $1,036.25   $1,036.10