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 $88.84   6.149%   $94.3028   $94.30   $94.30   $94.30  
  Purchase #2 $138.96   6.356%   $147.7923   $147.79   $147.80   $147.80  
  Purchase #3 $160.90   3.761%   $166.9514   $166.95   $166.95   $167.00  
  Purchase #4 $30.35   6.258%   $32.2493   $32.25   $32.25   $32.20  
  Purchase #5 $59.71   12.797%   $67.3511   $67.35   $67.35   $67.40  
  Purchase #6 $14.63   5.862%   $15.4876   $15.49   $15.50   $15.50  
  Purchase #7 $188.98   13.177%   $213.8819   $213.88   $213.90   $213.90  
  7 purchase totals = $682.37       $738.0164   $738.01   $738.05   $738.10