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 $23.53   3.117%   $24.2634   $24.26   $24.25   $24.30  
  Purchase #2 $69.43   8.512%   $75.3399   $75.34   $75.35   $75.30  
  Purchase #3 $180.90   13.326%   $205.0067   $205.01   $205.00   $205.00  
  Purchase #4 $209.44   5.749%   $221.4807   $221.48   $221.50   $221.50  
  Purchase #5 $59.64   9.806%   $65.4883   $65.49   $65.50   $65.50  
  Purchase #6 $241.87   13.434%   $274.3628   $274.36   $274.35   $274.40  
  Purchase #7 $239.37   7.611%   $257.5885   $257.59   $257.60   $257.60  
  7 purchase totals = $1,024.18       $1,123.5303   $1,123.53   $1,123.55   $1,123.60