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 $193.98   10.296%   $213.9522   $213.95   $213.95   $214.00  
  Purchase #2 $208.81   7.581%   $224.6399   $224.64   $224.65   $224.60  
  Purchase #3 $131.79   12.132%   $147.7788   $147.78   $147.80   $147.80  
  Purchase #4 $98.84   6.520%   $105.2844   $105.28   $105.30   $105.30  
  Purchase #5 $153.97   5.310%   $162.1458   $162.15   $162.15   $162.10  
  Purchase #6 $144.71   6.592%   $154.2493   $154.25   $154.25   $154.20  
  Purchase #7 $41.67   6.422%   $44.346   $44.35   $44.35   $44.30  
  7 purchase totals = $973.77       $1,052.3964   $1,052.40   $1,052.45   $1,052.30