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 $49.69   9.272%   $54.2973   $54.30   $54.30   $54.30  
  Purchase #2 $167.29   5.611%   $176.6766   $176.68   $176.70   $176.70  
  Purchase #3 $192.77   12.607%   $217.0725   $217.07   $217.05   $217.10  
  Purchase #4 $214.56   5.460%   $226.275   $226.28   $226.30   $226.30  
  Purchase #5 $57.61   6.617%   $61.4221   $61.42   $61.40   $61.40  
  Purchase #6 $105.84   4.429%   $110.5277   $110.53   $110.55   $110.50  
  Purchase #7 $103.42   12.742%   $116.5978   $116.60   $116.60   $116.60  
  7 purchase totals = $891.18       $962.8690   $962.88   $962.90   $962.90