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 $183.71   10.300%   $202.6321   $202.63   $202.65   $202.60  
  Purchase #2 $104.57   3.215%   $107.9319   $107.93   $107.95   $107.90  
  Purchase #3 $228.68   9.277%   $249.8946   $249.89   $249.90   $249.90  
  Purchase #4 $77.67   10.333%   $85.6956   $85.70   $85.70   $85.70  
  Purchase #5 $129.37   11.436%   $144.1648   $144.16   $144.15   $144.20  
  Purchase #6 $18.54   10.725%   $20.5284   $20.53   $20.55   $20.50  
  Purchase #7 $237.29   5.766%   $250.9721   $250.97   $250.95   $251.00  
  7 purchase totals = $979.83       $1,061.8195   $1,061.81   $1,061.85   $1,061.80