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	$37.39	9.499%	$40.9417	$40.94	$40.95	$40.90
Purchase #2	$29.59	12.808%	$33.3799	$33.38	$33.40	$33.40
Purchase #3	$57.46	9.665%	$63.0135	$63.01	$63.00	$63.00
Purchase #4	$24.48	3.408%	$25.3143	$25.31	$25.30	$25.30
Purchase #5	$158.35	8.223%	$171.3711	$171.37	$171.35	$171.40
Purchase #6	$83.71	8.604%	$90.9124	$90.91	$90.90	$90.90
Purchase #7	$156.45	11.671%	$174.7093	$174.71	$174.70	$174.70
7 purchase totals =	$547.43		$599.6422	$599.63	$599.60	$599.60