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 $193.45   5.448%   $203.9892   $203.99   $204.00   $204.00  
  Purchase #2 $185.52   4.389%   $193.6625   $193.66   $193.65   $193.70  
  Purchase #3 $123.35   3.180%   $127.2725   $127.27   $127.25   $127.30  
  Purchase #4 $215.67   9.821%   $236.851   $236.85   $236.85   $236.90  
  Purchase #5 $183.73   7.481%   $197.4748   $197.47   $197.45   $197.50  
  Purchase #6 $250.86   13.671%   $285.1551   $285.16   $285.15   $285.20  
  Purchase #7 $230.61   7.328%   $247.5091   $247.51   $247.50   $247.50  
  7 purchase totals = $1,383.19       $1,491.9142   $1,491.91   $1,491.85   $1,492.10