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 $65.90   5.549%   $69.5568   $69.56   $69.55   $69.60  
  Purchase #2 $108.53   8.102%   $117.3231   $117.32   $117.30   $117.30  
  Purchase #3 $245.71   9.353%   $268.6913   $268.69   $268.70   $268.70  
  Purchase #4 $193.49   3.732%   $200.711   $200.71   $200.70   $200.70  
  Purchase #5 $201.87   7.303%   $216.6126   $216.61   $216.60   $216.60  
  Purchase #6 $211.87   3.562%   $219.4168   $219.42   $219.40   $219.40  
  Purchase #7 $229.63   5.654%   $242.6133   $242.61   $242.60   $242.60  
  7 purchase totals = $1,257.00       $1,334.9249   $1,334.92   $1,334.85   $1,334.90