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 $193.87   9.470%   $212.2295   $212.23   $212.25   $212.20  
  Purchase #2 $214.56   8.200%   $232.1539   $232.15   $232.15   $232.20  
  Purchase #3 $237.58   7.249%   $254.8022   $254.80   $254.80   $254.80  
  Purchase #4 $194.72   11.608%   $217.3231   $217.32   $217.30   $217.30  
  Purchase #5 $46.61   7.126%   $49.9314   $49.93   $49.95   $49.90  
  Purchase #6 $173.44   13.514%   $196.8787   $196.88   $196.90   $196.90  
  Purchase #7 $166.86   11.467%   $185.9938   $185.99   $186.00   $186.00  
  7 purchase totals = $1,227.64       $1,349.3126   $1,349.30   $1,349.35   $1,349.30