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 $24.48   9.290%   $26.7542   $26.75   $26.75   $26.80  
  Purchase #2 $198.68   13.191%   $224.8879   $224.89   $224.90   $224.90  
  Purchase #3 $42.63   7.332%   $45.7556   $45.76   $45.75   $45.80  
  Purchase #4 $222.61   6.694%   $237.5115   $237.51   $237.50   $237.50  
  Purchase #5 $89.37   9.558%   $97.912   $97.91   $97.90   $97.90  
  Purchase #6 $168.45   6.231%   $178.9461   $178.95   $178.95   $178.90  
  Purchase #7 $207.68   9.108%   $226.5955   $226.60   $226.60   $226.60  
  7 purchase totals = $953.90       $1,038.3628   $1,038.37   $1,038.35   $1,038.40