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	$222.52	5.584%	$234.9455	$234.95	$234.95	$234.90
Purchase #2	$90.76	13.376%	$102.9001	$102.90	$102.90	$102.90
Purchase #3	$10.57	10.250%	$11.6534	$11.65	$11.65	$11.70
Purchase #4	$31.89	13.536%	$36.2066	$36.21	$36.20	$36.20
Purchase #5	$197.48	13.319%	$223.7824	$223.78	$223.80	$223.80
Purchase #6	$178.73	5.422%	$188.4207	$188.42	$188.40	$188.40
Purchase #7	$42.39	6.813%	$45.278	$45.28	$45.30	$45.30
7 purchase totals =	$774.34		$843.1867	$843.19	$843.20	$843.20