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 $224.97   7.282%   $241.3523   $241.35   $241.35   $241.40  
  Purchase #2 $25.99   6.586%   $27.7017   $27.70   $27.70   $27.70  
  Purchase #3 $20.68   8.256%   $22.3873   $22.39   $22.40   $22.40  
  Purchase #4 $45.94   6.513%   $48.9321   $48.93   $48.95   $48.90  
  Purchase #5 $147.75   9.815%   $162.2517   $162.25   $162.25   $162.30  
  Purchase #6 $194.76   4.135%   $202.8133   $202.81   $202.80   $202.80  
  Purchase #7 $214.49   5.594%   $226.4886   $226.49   $226.50   $226.50  
  7 purchase totals = $874.58       $931.9270   $931.92   $931.95   $932.00