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 $54.63   5.829%   $57.8144   $57.81   $57.80   $57.80  
  Purchase #2 $99.30   9.352%   $108.5865   $108.59   $108.60   $108.60  
  Purchase #3 $176.54   3.525%   $182.763   $182.76   $182.75   $182.80  
  Purchase #4 $161.62   7.212%   $173.276   $173.28   $173.30   $173.30  
  Purchase #5 $100.31   9.469%   $109.8084   $109.81   $109.80   $109.80  
  Purchase #6 $225.49   11.212%   $250.7719   $250.77   $250.75   $250.80  
  Purchase #7 $69.78   7.352%   $74.9102   $74.91   $74.90   $74.90  
  7 purchase totals = $887.67       $957.9304   $957.93   $957.90   $958.00