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	$54.30	7.768%	$58.518	$58.52	$58.50	$58.50
Purchase #2	$45.86	9.545%	$50.2373	$50.24	$50.25	$50.20
Purchase #3	$105.99	4.753%	$111.0277	$111.03	$111.05	$111.00
Purchase #4	$94.56	7.396%	$101.5537	$101.55	$101.55	$101.60
Purchase #5	$246.71	11.421%	$274.8867	$274.89	$274.90	$274.90
Purchase #6	$198.66	5.140%	$208.8711	$208.87	$208.85	$208.90
Purchase #7	$49.28	3.130%	$50.8225	$50.82	$50.80	$50.80
7 purchase totals =	$795.36		$855.9170	$855.92	$855.90	$855.90