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	$243.90	12.251%	$273.7802	$273.78	$273.80	$273.80
Purchase #2	$42.33	3.268%	$43.7133	$43.71	$43.70	$43.70
Purchase #3	$186.26	10.588%	$205.9812	$205.98	$206.00	$206.00
Purchase #4	$132.30	6.696%	$141.1588	$141.16	$141.15	$141.20
Purchase #5	$100.84	6.713%	$107.6094	$107.61	$107.60	$107.60
Purchase #6	$32.44	7.539%	$34.8857	$34.89	$34.90	$34.90
Purchase #7	$77.39	6.135%	$82.1379	$82.14	$82.15	$82.10
7 purchase totals =	$815.46		$889.2665	$889.27	$889.30	$889.30