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	$86.82	11.258%	$96.5942	$96.59	$96.60	$96.60
Purchase #2	$169.86	3.475%	$175.7626	$175.76	$175.75	$175.80
Purchase #3	$141.27	6.240%	$150.0852	$150.09	$150.10	$150.10
Purchase #4	$84.83	6.522%	$90.3626	$90.36	$90.35	$90.40
Purchase #5	$70.53	7.386%	$75.7393	$75.74	$75.75	$75.70
Purchase #6	$97.58	13.855%	$111.0997	$111.10	$111.10	$111.10
Purchase #7	$68.72	8.839%	$74.7942	$74.79	$74.80	$74.80
7 purchase totals =	$719.61		$774.4378	$774.43	$774.45	$774.50