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 $23.34   5.807%   $24.6954   $24.70   $24.70   $24.70  
  Purchase #2 $243.88   13.819%   $277.5818   $277.58   $277.60   $277.60  
  Purchase #3 $115.79   8.273%   $125.3693   $125.37   $125.35   $125.40  
  Purchase #4 $192.66   3.477%   $199.3588   $199.36   $199.35   $199.40  
  Purchase #5 $107.93   4.226%   $112.4911   $112.49   $112.50   $112.50  
  Purchase #6 $232.63   9.113%   $253.8296   $253.83   $253.85   $253.80  
  Purchase #7 $240.30   4.402%   $250.878   $250.88   $250.90   $250.90  
  7 purchase totals = $1,156.53       $1,244.2040   $1,244.21   $1,244.25   $1,244.30