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 $55.33   11.715%   $61.8119   $61.81   $61.80   $61.80  
  Purchase #2 $125.92   11.709%   $140.664   $140.66   $140.65   $140.70  
  Purchase #3 $27.76   5.456%   $29.2746   $29.27   $29.25   $29.30  
  Purchase #4 $215.87   5.782%   $228.3516   $228.35   $228.35   $228.40  
  Purchase #5 $80.88   4.601%   $84.6013   $84.60   $84.60   $84.60  
  Purchase #6 $164.82   3.778%   $171.0469   $171.05   $171.05   $171.00  
  Purchase #7 $82.64   6.643%   $88.1298   $88.13   $88.15   $88.10  
  7 purchase totals = $753.22       $803.8801   $803.87   $803.85   $803.90