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 $129.32   11.763%   $144.5319   $144.53   $144.55   $144.50  
  Purchase #2 $158.72   11.311%   $176.6728   $176.67   $176.65   $176.70  
  Purchase #3 $203.86   5.419%   $214.9072   $214.91   $214.90   $214.90  
  Purchase #4 $99.34   4.841%   $104.149   $104.15   $104.15   $104.10  
  Purchase #5 $192.76   8.411%   $208.973   $208.97   $208.95   $209.00  
  Purchase #6 $151.47   11.330%   $168.6316   $168.63   $168.65   $168.60  
  Purchase #7 $207.30   11.275%   $230.6731   $230.67   $230.65   $230.70  
  7 purchase totals = $1,142.77       $1,248.5386   $1,248.53   $1,248.50   $1,248.50