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	$19.97	10.282%	$22.0233	$22.02	$22.00	$22.00
Purchase #2	$194.88	10.472%	$215.2878	$215.29	$215.30	$215.30
Purchase #3	$172.93	4.176%	$180.1516	$180.15	$180.15	$180.20
Purchase #4	$149.87	10.735%	$165.9585	$165.96	$165.95	$166.00
Purchase #5	$56.33	7.349%	$60.4697	$60.47	$60.45	$60.50
Purchase #6	$111.47	7.415%	$119.7355	$119.74	$119.75	$119.70
Purchase #7	$69.59	13.355%	$78.8837	$78.88	$78.90	$78.90
7 purchase totals =	$775.04		$842.5101	$842.51	$842.50	$842.60