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 $67.65   12.203%   $75.9053   $75.91   $75.90   $75.90  
  Purchase #2 $221.35   11.805%   $247.4804   $247.48   $247.50   $247.50  
  Purchase #3 $50.35   9.771%   $55.2697   $55.27   $55.25   $55.30  
  Purchase #4 $221.97   9.193%   $242.3757   $242.38   $242.40   $242.40  
  Purchase #5 $206.71   3.806%   $214.5774   $214.58   $214.60   $214.60  
  Purchase #6 $172.68   5.709%   $182.5383   $182.54   $182.55   $182.50  
  Purchase #7 $204.98   6.733%   $218.7813   $218.78   $218.80   $218.80  
  7 purchase totals = $1,145.69       $1,236.9281   $1,236.94   $1,237.00   $1,237.00