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	$88.56	13.521%	$100.5342	$100.53	$100.55	$100.50
Purchase #2	$41.48	5.502%	$43.7622	$43.76	$43.75	$43.80
Purchase #3	$147.59	11.533%	$164.6116	$164.61	$164.60	$164.60
Purchase #4	$127.36	11.638%	$142.1822	$142.18	$142.20	$142.20
Purchase #5	$110.30	10.767%	$122.176	$122.18	$122.20	$122.20
Purchase #6	$75.67	5.858%	$80.1027	$80.10	$80.10	$80.10
Purchase #7	$226.66	9.643%	$248.5168	$248.52	$248.50	$248.50
7 purchase totals =	$817.62		$901.8857	$901.88	$901.90	$901.90