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 $119.32   4.219%   $124.3541   $124.35   $124.35   $124.40  
  Purchase #2 $127.37   12.111%   $142.7958   $142.80   $142.80   $142.80  
  Purchase #3 $201.35   6.823%   $215.0881   $215.09   $215.10   $215.10  
  Purchase #4 $179.93   3.644%   $186.4866   $186.49   $186.50   $186.50  
  Purchase #5 $67.59   8.301%   $73.2006   $73.20   $73.20   $73.20  
  Purchase #6 $187.53   4.429%   $195.8357   $195.84   $195.85   $195.80  
  Purchase #7 $11.60   13.260%   $13.1382   $13.14   $13.15   $13.10  
  7 purchase totals = $894.69       $950.8991   $950.91   $950.95   $950.90