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 $52.95   13.694%   $60.201   $60.20   $60.20   $60.20  
  Purchase #2 $200.96   11.825%   $224.7235   $224.72   $224.70   $224.70  
  Purchase #3 $47.42   4.182%   $49.4031   $49.40   $49.40   $49.40  
  Purchase #4 $5.67   8.433%   $6.1482   $6.15   $6.15   $6.10  
  Purchase #5 $103.76   13.301%   $117.5611   $117.56   $117.55   $117.60  
  Purchase #6 $10.80   13.265%   $12.2326   $12.23   $12.25   $12.20  
  Purchase #7 $238.92   8.609%   $259.4886   $259.49   $259.50   $259.50  
  7 purchase totals = $660.48       $729.7581   $729.75   $729.75   $729.70