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 $95.64   13.237%   $108.2999   $108.30   $108.30   $108.30  
  Purchase #2 $248.95   8.360%   $269.7622   $269.76   $269.75   $269.80  
  Purchase #3 $94.68   3.559%   $98.0497   $98.05   $98.05   $98.00  
  Purchase #4 $62.90   3.330%   $64.9946   $64.99   $65.00   $65.00  
  Purchase #5 $191.66   7.272%   $205.5975   $205.60   $205.60   $205.60  
  Purchase #6 $74.65   5.422%   $78.6975   $78.70   $78.70   $78.70  
  Purchase #7 $181.86   7.195%   $194.9448   $194.94   $194.95   $194.90  
  7 purchase totals = $950.34       $1,020.3462   $1,020.34   $1,020.35   $1,020.30