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	$48.50	4.467%	$50.6665	$50.67	$50.65	$50.70
Purchase #2	$146.41	12.569%	$164.8123	$164.81	$164.80	$164.80
Purchase #3	$146.57	10.583%	$162.0815	$162.08	$162.10	$162.10
Purchase #4	$45.42	5.480%	$47.909	$47.91	$47.90	$47.90
Purchase #5	$203.75	9.344%	$222.7884	$222.79	$222.80	$222.80
Purchase #6	$120.39	5.611%	$127.1451	$127.15	$127.15	$127.10
Purchase #7	$164.33	12.713%	$185.2213	$185.22	$185.20	$185.20
7 purchase totals =	$875.37		$960.6241	$960.63	$960.60	$960.60