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 $47.56   3.571%   $49.2584   $49.26   $49.25   $49.30  
  Purchase #2 $58.89   13.408%   $66.786   $66.79   $66.80   $66.80  
  Purchase #3 $133.76   7.823%   $144.224   $144.22   $144.20   $144.20  
  Purchase #4 $233.55   13.414%   $264.8784   $264.88   $264.90   $264.90  
  Purchase #5 $117.58   6.339%   $125.0334   $125.03   $125.05   $125.00  
  Purchase #6 $166.62   9.795%   $182.9404   $182.94   $182.95   $182.90  
  Purchase #7 $168.81   4.558%   $176.5044   $176.50   $176.50   $176.50  
  7 purchase totals = $926.77       $1,009.6250   $1,009.62   $1,009.65   $1,009.60