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	$245.38	9.800%	$269.4272	$269.43	$269.45	$269.40
Purchase #2	$229.39	12.592%	$258.2748	$258.27	$258.25	$258.30
Purchase #3	$223.37	11.304%	$248.6197	$248.62	$248.60	$248.60
Purchase #4	$171.30	7.243%	$183.7073	$183.71	$183.70	$183.70
Purchase #5	$150.57	9.790%	$165.3108	$165.31	$165.30	$165.30
Purchase #6	$216.52	10.318%	$238.8605	$238.86	$238.85	$238.90
Purchase #7	$139.99	4.782%	$146.6843	$146.68	$146.70	$146.70
7 purchase totals =	$1,376.52		$1,510.8846	$1,510.88	$1,510.85	$1,510.90