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	$136.46	6.632%	$145.51	$145.51	$145.50	$145.50
Purchase #2	$15.80	10.713%	$17.4927	$17.49	$17.50	$17.50
Purchase #3	$134.71	12.642%	$151.74	$151.74	$151.75	$151.70
Purchase #4	$11.69	9.391%	$12.7878	$12.79	$12.80	$12.80
Purchase #5	$83.32	4.717%	$87.2502	$87.25	$87.25	$87.30
Purchase #6	$225.40	13.458%	$255.7343	$255.73	$255.75	$255.70
Purchase #7	$79.35	12.695%	$89.4235	$89.42	$89.40	$89.40
7 purchase totals =	$686.73		$759.9385	$759.93	$759.95	$759.90