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	$29.73	3.874%	$30.8817	$30.88	$30.90	$30.90
Purchase #2	$194.96	8.487%	$211.5063	$211.51	$211.50	$211.50
Purchase #3	$155.32	12.362%	$174.5207	$174.52	$174.50	$174.50
Purchase #4	$34.41	3.800%	$35.7176	$35.72	$35.70	$35.70
Purchase #5	$136.78	6.705%	$145.9511	$145.95	$145.95	$146.00
Purchase #6	$40.88	12.200%	$45.8674	$45.87	$45.85	$45.90
Purchase #7	$91.38	9.277%	$99.8573	$99.86	$99.85	$99.90
7 purchase totals =	$683.46		$744.3021	$744.31	$744.25	$744.40