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 $117.57   5.857%   $124.4561   $124.46   $124.45   $124.50  
  Purchase #2 $250.43   7.272%   $268.6413   $268.64   $268.65   $268.60  
  Purchase #3 $15.65   7.155%   $16.7698   $16.77   $16.75   $16.80  
  Purchase #4 $9.55   12.436%   $10.7376   $10.74   $10.75   $10.70  
  Purchase #5 $125.81   11.580%   $140.3788   $140.38   $140.40   $140.40  
  Purchase #6 $9.93   13.492%   $11.2698   $11.27   $11.25   $11.30  
  Purchase #7 $165.28   8.529%   $179.3767   $179.38   $179.40   $179.40  
  7 purchase totals = $694.22       $751.6301   $751.64   $751.65   $751.70