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	$38.75	10.233%	$42.7153	$42.72	$42.70	$42.70
Purchase #2	$96.96	8.709%	$105.4042	$105.40	$105.40	$105.40
Purchase #3	$193.75	10.805%	$214.6847	$214.68	$214.70	$214.70
Purchase #4	$39.72	3.114%	$40.9569	$40.96	$40.95	$41.00
Purchase #5	$55.56	13.764%	$63.2073	$63.21	$63.20	$63.20
Purchase #6	$171.43	11.606%	$191.3262	$191.33	$191.35	$191.30
Purchase #7	$186.59	7.394%	$200.3865	$200.39	$200.40	$200.40
7 purchase totals =	$782.76		$858.6811	$858.69	$858.70	$858.70