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 $194.77   5.661%   $205.7959   $205.80   $205.80   $205.80  
  Purchase #2 $61.25   12.118%   $68.6723   $68.67   $68.65   $68.70  
  Purchase #3 $55.81   3.617%   $57.8286   $57.83   $57.85   $57.80  
  Purchase #4 $62.31   3.357%   $64.4017   $64.40   $64.40   $64.40  
  Purchase #5 $93.74   11.407%   $104.4329   $104.43   $104.45   $104.40  
  Purchase #6 $206.73   5.706%   $218.526   $218.53   $218.55   $218.50  
  Purchase #7 $83.29   11.367%   $92.7576   $92.76   $92.75   $92.80  
  7 purchase totals = $757.90       $812.4150   $812.42   $812.45   $812.40