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 $95.27   6.277%   $101.2501   $101.25   $101.25   $101.30  
  Purchase #2 $176.94   4.190%   $184.3538   $184.35   $184.35   $184.40  
  Purchase #3 $181.98   10.612%   $201.2917   $201.29   $201.30   $201.30  
  Purchase #4 $111.71   6.684%   $119.1767   $119.18   $119.20   $119.20  
  Purchase #5 $222.95   10.212%   $245.7177   $245.72   $245.70   $245.70  
  Purchase #6 $15.36   7.472%   $16.5077   $16.51   $16.50   $16.50  
  Purchase #7 $125.49   6.727%   $133.9317   $133.93   $133.95   $133.90  
  7 purchase totals = $929.70       $1,002.2294   $1,002.23   $1,002.25   $1,002.30