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 $66.43   12.623%   $74.8155   $74.82   $74.80   $74.80  
  Purchase #2 $226.85   9.194%   $247.7066   $247.71   $247.70   $247.70  
  Purchase #3 $48.28   8.330%   $52.3017   $52.30   $52.30   $52.30  
  Purchase #4 $59.81   10.340%   $65.9944   $65.99   $66.00   $66.00  
  Purchase #5 $17.62   5.711%   $18.6263   $18.63   $18.65   $18.60  
  Purchase #6 $232.72   13.669%   $264.5305   $264.53   $264.55   $264.50  
  Purchase #7 $70.96   10.546%   $78.4434   $78.44   $78.45   $78.40  
  7 purchase totals = $722.67       $802.4184   $802.42   $802.45   $802.30