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 $215.94   6.303%   $229.5507   $229.55   $229.55   $229.60  
  Purchase #2 $46.76   6.511%   $49.8045   $49.80   $49.80   $49.80  
  Purchase #3 $148.87   3.619%   $154.2576   $154.26   $154.25   $154.30  
  Purchase #4 $121.70   13.357%   $137.9555   $137.96   $137.95   $138.00  
  Purchase #5 $73.38   6.485%   $78.1387   $78.14   $78.15   $78.10  
  Purchase #6 $183.32   13.180%   $207.4816   $207.48   $207.50   $207.50  
  Purchase #7 $154.58   8.461%   $167.659   $167.66   $167.65   $167.70  
  7 purchase totals = $944.55       $1,024.8476   $1,024.85   $1,024.85   $1,025.00