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 $67.66   13.104%   $76.5262   $76.53   $76.55   $76.50  
  Purchase #2 $160.90   7.163%   $172.4253   $172.43   $172.45   $172.40  
  Purchase #3 $64.70   6.702%   $69.0362   $69.04   $69.05   $69.00  
  Purchase #4 $213.42   6.515%   $227.3243   $227.32   $227.30   $227.30  
  Purchase #5 $68.30   10.295%   $75.3315   $75.33   $75.35   $75.30  
  Purchase #6 $73.68   13.853%   $83.8869   $83.89   $83.90   $83.90  
  Purchase #7 $233.75   9.249%   $255.3695   $255.37   $255.35   $255.40  
  7 purchase totals = $882.41       $959.8999   $959.91   $959.95   $959.80