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 $113.30   4.112%   $117.9589   $117.96   $117.95   $118.00  
  Purchase #2 $162.69   13.415%   $184.5149   $184.51   $184.50   $184.50  
  Purchase #3 $188.57   11.836%   $210.8891   $210.89   $210.90   $210.90  
  Purchase #4 $233.97   11.641%   $261.2064   $261.21   $261.20   $261.20  
  Purchase #5 $159.60   7.361%   $171.3482   $171.35   $171.35   $171.30  
  Purchase #6 $112.61   3.532%   $116.5874   $116.59   $116.60   $116.60  
  Purchase #7 $50.99   9.178%   $55.6699   $55.67   $55.65   $55.70  
  7 purchase totals = $1,021.73       $1,118.1748   $1,118.18   $1,118.15   $1,118.20