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 $72.64   5.613%   $76.7173   $76.72   $76.70   $76.70  
  Purchase #2 $214.94   8.544%   $233.3045   $233.30   $233.30   $233.30  
  Purchase #3 $229.54   12.640%   $258.5539   $258.55   $258.55   $258.60  
  Purchase #4 $195.50   12.854%   $220.6296   $220.63   $220.65   $220.60  
  Purchase #5 $65.61   4.748%   $68.7252   $68.73   $68.75   $68.70  
  Purchase #6 $190.92   13.369%   $216.4441   $216.44   $216.45   $216.40  
  Purchase #7 $110.72   3.689%   $114.8045   $114.80   $114.80   $114.80  
  7 purchase totals = $1,079.87       $1,189.1791   $1,189.17   $1,189.20   $1,189.10