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	$248.82	6.264%	$264.4061	$264.41	$264.40	$264.40
Purchase #2	$55.93	5.782%	$59.1639	$59.16	$59.15	$59.20
Purchase #3	$118.62	4.792%	$124.3043	$124.30	$124.30	$124.30
Purchase #4	$231.53	5.403%	$244.0396	$244.04	$244.05	$244.00
Purchase #5	$205.71	12.324%	$231.0617	$231.06	$231.05	$231.10
Purchase #6	$107.53	6.692%	$114.7259	$114.73	$114.75	$114.70
Purchase #7	$99.38	12.286%	$111.5898	$111.59	$111.60	$111.60
7 purchase totals =	$1,067.52		$1,149.2913	$1,149.29	$1,149.30	$1,149.30