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 $220.49   8.686%   $239.6418   $239.64   $239.65   $239.60  
  Purchase #2 $111.85   12.365%   $125.6803   $125.68   $125.70   $125.70  
  Purchase #3 $117.88   13.676%   $134.0013   $134.00   $134.00   $134.00  
  Purchase #4 $154.68   6.470%   $164.6878   $164.69   $164.70   $164.70  
  Purchase #5 $87.88   5.561%   $92.767   $92.77   $92.75   $92.80  
  Purchase #6 $223.87   9.658%   $245.4914   $245.49   $245.50   $245.50  
  Purchase #7 $199.62   4.365%   $208.3334   $208.33   $208.35   $208.30  
  7 purchase totals = $1,116.27       $1,210.6030   $1,210.60   $1,210.65   $1,210.60