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	$151.71	4.663%	$158.7842	$158.78	$158.80	$158.80
Purchase #2	$149.65	6.432%	$159.2755	$159.28	$159.30	$159.30
Purchase #3	$31.61	5.392%	$33.3144	$33.31	$33.30	$33.30
Purchase #4	$103.26	7.707%	$111.2182	$111.22	$111.20	$111.20
Purchase #5	$43.63	9.676%	$47.8516	$47.85	$47.85	$47.90
Purchase #6	$100.78	11.574%	$112.4443	$112.44	$112.45	$112.40
Purchase #7	$41.41	9.447%	$45.322	$45.32	$45.30	$45.30
7 purchase totals =	$622.05		$668.2102	$668.20	$668.20	$668.20