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	$78.43	12.357%	$88.1216	$88.12	$88.10	$88.10
Purchase #2	$62.40	7.773%	$67.2504	$67.25	$67.25	$67.30
Purchase #3	$62.82	10.662%	$69.5179	$69.52	$69.50	$69.50
Purchase #4	$26.51	11.197%	$29.4783	$29.48	$29.50	$29.50
Purchase #5	$86.86	3.378%	$89.7941	$89.79	$89.80	$89.80
Purchase #6	$167.80	4.178%	$174.8107	$174.81	$174.80	$174.80
Purchase #7	$74.26	4.447%	$77.5623	$77.56	$77.55	$77.60
7 purchase totals =	$559.08		$596.5353	$596.53	$596.50	$596.60