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	$73.59	6.599%	$78.4462	$78.45	$78.45	$78.40
Purchase #2	$129.48	13.583%	$147.0673	$147.07	$147.05	$147.10
Purchase #3	$109.59	8.181%	$118.5556	$118.56	$118.55	$118.60
Purchase #4	$73.32	7.370%	$78.7237	$78.72	$78.70	$78.70
Purchase #5	$231.35	9.663%	$253.7054	$253.71	$253.70	$253.70
Purchase #6	$44.35	3.515%	$45.9089	$45.91	$45.90	$45.90
Purchase #7	$134.92	6.864%	$144.1809	$144.18	$144.20	$144.20
7 purchase totals =	$796.60		$866.5880	$866.60	$866.55	$866.60