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	$51.72	6.147%	$54.8992	$54.90	$54.90	$54.90
Purchase #2	$29.53	9.148%	$32.2314	$32.23	$32.25	$32.20
Purchase #3	$186.87	13.184%	$211.5069	$211.51	$211.50	$211.50
Purchase #4	$93.51	12.454%	$105.1557	$105.16	$105.15	$105.20
Purchase #5	$119.41	4.118%	$124.3273	$124.33	$124.35	$124.30
Purchase #6	$244.59	7.602%	$263.1837	$263.18	$263.20	$263.20
Purchase #7	$250.49	13.413%	$284.0882	$284.09	$284.10	$284.10
7 purchase totals =	$976.12		$1,075.3924	$1,075.40	$1,075.45	$1,075.40