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 $111.98   12.564%   $126.0492   $126.05   $126.05   $126.00  
  Purchase #2 $44.61   9.216%   $48.7213   $48.72   $48.70   $48.70  
  Purchase #3 $242.47   12.853%   $273.6347   $273.63   $273.65   $273.60  
  Purchase #4 $161.76   5.436%   $170.5533   $170.55   $170.55   $170.60  
  Purchase #5 $89.25   13.527%   $101.3228   $101.32   $101.30   $101.30  
  Purchase #6 $137.63   4.816%   $144.2583   $144.26   $144.25   $144.30  
  Purchase #7 $233.65   8.356%   $253.1738   $253.17   $253.15   $253.20  
  7 purchase totals = $1,021.35       $1,117.7134   $1,117.70   $1,117.65   $1,117.70