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	$223.74	11.179%	$248.7519	$248.75	$248.75	$248.80
Purchase #2	$228.75	5.855%	$242.1433	$242.14	$242.15	$242.10
Purchase #3	$188.37	10.582%	$208.3033	$208.30	$208.30	$208.30
Purchase #4	$207.85	7.125%	$222.6593	$222.66	$222.65	$222.70
Purchase #5	$66.84	4.796%	$70.0456	$70.05	$70.05	$70.00
Purchase #6	$99.81	11.800%	$111.5876	$111.59	$111.60	$111.60
Purchase #7	$140.28	7.120%	$150.2679	$150.27	$150.25	$150.30
7 purchase totals =	$1,155.64		$1,253.7589	$1,253.76	$1,253.75	$1,253.80