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	$53.43	6.873%	$57.1022	$57.10	$57.10	$57.10
Purchase #2	$89.39	5.316%	$94.142	$94.14	$94.15	$94.10
Purchase #3	$23.79	11.487%	$26.5228	$26.52	$26.50	$26.50
Purchase #4	$19.40	10.242%	$21.3869	$21.39	$21.40	$21.40
Purchase #5	$78.94	11.810%	$88.2628	$88.26	$88.25	$88.30
Purchase #6	$72.98	7.440%	$78.4097	$78.41	$78.40	$78.40
Purchase #7	$227.74	12.403%	$255.9866	$255.99	$256.00	$256.00
7 purchase totals =	$565.67		$621.8130	$621.81	$621.80	$621.80