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 $213.49   12.134%   $239.3949   $239.39   $239.40   $239.40  
  Purchase #2 $216.82   13.246%   $245.54   $245.54   $245.55   $245.50  
  Purchase #3 $153.89   12.413%   $172.9924   $172.99   $173.00   $173.00  
  Purchase #4 $79.55   4.767%   $83.3421   $83.34   $83.35   $83.30  
  Purchase #5 $198.31   8.183%   $214.5377   $214.54   $214.55   $214.50  
  Purchase #6 $111.53   12.754%   $125.7545   $125.75   $125.75   $125.80  
  Purchase #7 $56.26   6.606%   $59.9765   $59.98   $60.00   $60.00  
  7 purchase totals = $1,029.85       $1,141.5381   $1,141.53   $1,141.60   $1,141.50