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	$39.45	7.185%	$42.2845	$42.28	$42.30	$42.30
Purchase #2	$104.36	6.538%	$111.1831	$111.18	$111.20	$111.20
Purchase #3	$25.33	4.152%	$26.3817	$26.38	$26.40	$26.40
Purchase #4	$93.73	10.652%	$103.7141	$103.71	$103.70	$103.70
Purchase #5	$155.49	6.502%	$165.6	$165.60	$165.60	$165.60
Purchase #6	$109.25	7.205%	$117.1215	$117.12	$117.10	$117.10
Purchase #7	$199.38	6.755%	$212.8481	$212.85	$212.85	$212.80
7 purchase totals =	$726.99		$779.1330	$779.12	$779.15	$779.10