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	$65.56	7.291%	$70.34	$70.34	$70.35	$70.30
Purchase #2	$143.80	6.332%	$152.9054	$152.91	$152.90	$152.90
Purchase #3	$55.66	7.695%	$59.943	$59.94	$59.95	$59.90
Purchase #4	$60.37	4.872%	$63.3112	$63.31	$63.30	$63.30
Purchase #5	$238.85	12.713%	$269.215	$269.22	$269.20	$269.20
Purchase #6	$149.27	6.479%	$158.9412	$158.94	$158.95	$158.90
Purchase #7	$127.32	3.404%	$131.654	$131.65	$131.65	$131.70
7 purchase totals =	$840.83		$906.3098	$906.31	$906.30	$906.20