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 $14.55   5.212%   $15.3083   $15.31   $15.30   $15.30  
  Purchase #2 $58.86   8.396%   $63.8019   $63.80   $63.80   $63.80  
  Purchase #3 $15.94   8.576%   $17.307   $17.31   $17.30   $17.30  
  Purchase #4 $82.38   6.246%   $87.5255   $87.53   $87.55   $87.50  
  Purchase #5 $185.80   6.805%   $198.4437   $198.44   $198.45   $198.40  
  Purchase #6 $125.72   4.830%   $131.7923   $131.79   $131.80   $131.80  
  Purchase #7 $233.37   11.465%   $260.1259   $260.13   $260.15   $260.10  
  7 purchase totals = $716.62       $774.3046   $774.31   $774.35   $774.20