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 $182.62   12.208%   $204.9142   $204.91   $204.90   $204.90  
  Purchase #2 $26.36   8.852%   $28.6934   $28.69   $28.70   $28.70  
  Purchase #3 $78.50   11.165%   $87.2645   $87.26   $87.25   $87.30  
  Purchase #4 $246.35   12.734%   $277.7202   $277.72   $277.70   $277.70  
  Purchase #5 $18.70   11.118%   $20.7791   $20.78   $20.80   $20.80  
  Purchase #6 $211.85   11.526%   $236.2678   $236.27   $236.25   $236.30  
  Purchase #7 $95.88   4.811%   $100.4928   $100.49   $100.50   $100.50  
  7 purchase totals = $860.26       $956.1320   $956.12   $956.10   $956.20