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 $45.69   13.115%   $51.6822   $51.68   $51.70   $51.70  
  Purchase #2 $157.55   12.308%   $176.9413   $176.94   $176.95   $176.90  
  Purchase #3 $123.59   3.532%   $127.9552   $127.96   $127.95   $128.00  
  Purchase #4 $197.27   5.555%   $208.2283   $208.23   $208.25   $208.20  
  Purchase #5 $118.40   8.224%   $128.1372   $128.14   $128.15   $128.10  
  Purchase #6 $60.59   3.850%   $62.9227   $62.92   $62.90   $62.90  
  Purchase #7 $37.35   6.723%   $39.861   $39.86   $39.85   $39.90  
  7 purchase totals = $740.44       $795.7279   $795.73   $795.75   $795.70