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 $214.62   8.675%   $233.2383   $233.24   $233.25   $233.20  
  Purchase #2 $54.85   4.417%   $57.2727   $57.27   $57.25   $57.30  
  Purchase #3 $88.33   7.302%   $94.7799   $94.78   $94.80   $94.80  
  Purchase #4 $62.45   11.511%   $69.6386   $69.64   $69.65   $69.60  
  Purchase #5 $147.34   13.138%   $166.6975   $166.70   $166.70   $166.70  
  Purchase #6 $35.73   4.595%   $37.3718   $37.37   $37.35   $37.40  
  Purchase #7 $12.47   12.611%   $14.0426   $14.04   $14.05   $14.00  
  7 purchase totals = $615.79       $673.0414   $673.04   $673.05   $673.00