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	$62.59	8.401%	$67.8482	$67.85	$67.85	$67.80
Purchase #2	$104.29	13.867%	$118.7519	$118.75	$118.75	$118.80
Purchase #3	$134.76	9.708%	$147.8425	$147.84	$147.85	$147.80
Purchase #4	$55.31	7.834%	$59.643	$59.64	$59.65	$59.60
Purchase #5	$49.74	4.737%	$52.0962	$52.10	$52.10	$52.10
Purchase #6	$73.72	7.813%	$79.4797	$79.48	$79.50	$79.50
Purchase #7	$58.95	12.174%	$66.1266	$66.13	$66.15	$66.10
7 purchase totals =	$539.36		$591.7881	$591.79	$591.85	$591.70