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 $56.92   6.496%   $60.6175   $60.62   $60.60   $60.60  
  Purchase #2 $246.32   5.612%   $260.1435   $260.14   $260.15   $260.10  
  Purchase #3 $215.25   13.642%   $244.6144   $244.61   $244.60   $244.60  
  Purchase #4 $199.99   13.598%   $227.1846   $227.18   $227.20   $227.20  
  Purchase #5 $118.89   11.666%   $132.7597   $132.76   $132.75   $132.80  
  Purchase #6 $176.38   8.492%   $191.3582   $191.36   $191.35   $191.40  
  Purchase #7 $245.30   7.406%   $263.4669   $263.47   $263.45   $263.50  
  7 purchase totals = $1,259.05       $1,380.1448   $1,380.14   $1,380.10   $1,380.20