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 $61.66   10.131%   $67.9068   $67.91   $67.90   $67.90  
  Purchase #2 $193.97   10.694%   $214.7132   $214.71   $214.70   $214.70  
  Purchase #3 $9.62   10.260%   $10.607   $10.61   $10.60   $10.60  
  Purchase #4 $195.93   9.533%   $214.608   $214.61   $214.60   $214.60  
  Purchase #5 $204.86   5.340%   $215.7995   $215.80   $215.80   $215.80  
  Purchase #6 $60.47   3.515%   $62.5955   $62.60   $62.60   $62.60  
  Purchase #7 $49.94   4.434%   $52.1543   $52.15   $52.15   $52.20  
  7 purchase totals = $776.45       $838.3843   $838.39   $838.35   $838.40