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 $245.85   6.245%   $261.2033   $261.20   $261.20   $261.20  
  Purchase #2 $250.97   11.197%   $279.0711   $279.07   $279.05   $279.10  
  Purchase #3 $103.93   12.341%   $116.756   $116.76   $116.75   $116.80  
  Purchase #4 $244.78   12.458%   $275.2747   $275.27   $275.25   $275.30  
  Purchase #5 $210.56   9.318%   $230.18   $230.18   $230.20   $230.20  
  Purchase #6 $231.51   4.147%   $241.1107   $241.11   $241.10   $241.10  
  Purchase #7 $5.95   6.332%   $6.3268   $6.33   $6.35   $6.30  
  7 purchase totals = $1,293.55       $1,409.9226   $1,409.92   $1,409.90   $1,410.00