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	$170.93	7.263%	$183.3446	$183.34	$183.35	$183.30
Purchase #2	$65.93	12.873%	$74.4172	$74.42	$74.40	$74.40
Purchase #3	$68.87	11.269%	$76.631	$76.63	$76.65	$76.60
Purchase #4	$94.54	5.868%	$100.0876	$100.09	$100.10	$100.10
Purchase #5	$101.55	9.807%	$111.509	$111.51	$111.50	$111.50
Purchase #6	$174.55	6.222%	$185.4105	$185.41	$185.40	$185.40
Purchase #7	$67.65	13.874%	$77.0358	$77.04	$77.05	$77.00
7 purchase totals =	$744.02		$808.4357	$808.44	$808.45	$808.30