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	$126.37	6.600%	$134.7104	$134.71	$134.70	$134.70
Purchase #2	$89.69	11.333%	$99.8546	$99.85	$99.85	$99.90
Purchase #3	$136.97	11.809%	$153.1448	$153.14	$153.15	$153.10
Purchase #4	$198.88	4.829%	$208.4839	$208.48	$208.50	$208.50
Purchase #5	$63.69	12.180%	$71.4474	$71.45	$71.45	$71.40
Purchase #6	$120.91	8.113%	$130.7194	$130.72	$130.70	$130.70
Purchase #7	$64.50	3.170%	$66.5447	$66.54	$66.55	$66.50
7 purchase totals =	$801.01		$864.9052	$864.89	$864.90	$864.80