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 $54.67   11.126%   $60.7526   $60.75   $60.75   $60.80  
  Purchase #2 $233.95   6.854%   $249.9849   $249.98   $250.00   $250.00  
  Purchase #3 $180.74   9.506%   $197.9211   $197.92   $197.90   $197.90  
  Purchase #4 $20.29   4.702%   $21.244   $21.24   $21.25   $21.20  
  Purchase #5 $156.30   5.378%   $164.7058   $164.71   $164.70   $164.70  
  Purchase #6 $244.48   10.223%   $269.4732   $269.47   $269.45   $269.50  
  Purchase #7 $86.34   4.367%   $90.1105   $90.11   $90.10   $90.10  
  7 purchase totals = $976.77       $1,054.1921   $1,054.18   $1,054.15   $1,054.20