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	$239.54	11.469%	$267.0128	$267.01	$267.00	$267.00
Purchase #2	$83.39	8.675%	$90.6241	$90.62	$90.60	$90.60
Purchase #3	$53.84	8.521%	$58.4277	$58.43	$58.45	$58.40
Purchase #4	$19.38	10.469%	$21.4089	$21.41	$21.40	$21.40
Purchase #5	$29.69	12.255%	$33.3285	$33.33	$33.35	$33.30
Purchase #6	$51.47	8.469%	$55.829	$55.83	$55.85	$55.80
Purchase #7	$140.49	11.498%	$156.6435	$156.64	$156.65	$156.60
7 purchase totals =	$617.80		$683.2745	$683.27	$683.30	$683.10