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	$233.43	7.258%	$250.3723	$250.37	$250.35	$250.40
Purchase #2	$179.89	10.506%	$198.7892	$198.79	$198.80	$198.80
Purchase #3	$76.64	3.289%	$79.1607	$79.16	$79.15	$79.20
Purchase #4	$244.80	5.664%	$258.6655	$258.67	$258.65	$258.70
Purchase #5	$80.66	11.311%	$89.7835	$89.78	$89.80	$89.80
Purchase #6	$223.95	13.652%	$254.5237	$254.52	$254.50	$254.50
Purchase #7	$179.91	6.615%	$191.811	$191.81	$191.80	$191.80
7 purchase totals =	$1,219.28		$1,323.1059	$1,323.10	$1,323.05	$1,323.20