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 $233.67   3.463%   $241.762   $241.76   $241.75   $241.80  
  Purchase #2 $86.69   12.712%   $97.71   $97.71   $97.70   $97.70  
  Purchase #3 $187.46   8.861%   $204.0708   $204.07   $204.05   $204.10  
  Purchase #4 $8.70   9.109%   $9.4925   $9.49   $9.50   $9.50  
  Purchase #5 $91.25   3.843%   $94.7567   $94.76   $94.75   $94.80  
  Purchase #6 $105.77   13.431%   $119.976   $119.98   $120.00   $120.00  
  Purchase #7 $14.60   8.710%   $15.8717   $15.87   $15.85   $15.90  
  7 purchase totals = $728.14       $783.6397   $783.64   $783.60   $783.80