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 $240.53   11.656%   $268.5662   $268.57   $268.55   $268.60  
  Purchase #2 $74.84   10.597%   $82.7708   $82.77   $82.75   $82.80  
  Purchase #3 $179.71   5.787%   $190.1098   $190.11   $190.10   $190.10  
  Purchase #4 $195.82   5.591%   $206.7683   $206.77   $206.75   $206.80  
  Purchase #5 $55.61   12.525%   $62.5752   $62.58   $62.60   $62.60  
  Purchase #6 $201.25   8.420%   $218.1953   $218.20   $218.20   $218.20  
  Purchase #7 $182.38   5.792%   $192.9434   $192.94   $192.95   $192.90  
  7 purchase totals = $1,130.14       $1,221.9290   $1,221.94   $1,221.90   $1,222.00