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	$248.78	9.117%	$271.4613	$271.46	$271.45	$271.50
Purchase #2	$57.53	3.559%	$59.5775	$59.58	$59.60	$59.60
Purchase #3	$243.31	6.694%	$259.5972	$259.60	$259.60	$259.60
Purchase #4	$146.77	5.157%	$154.3389	$154.34	$154.35	$154.30
Purchase #5	$134.44	11.487%	$149.8831	$149.88	$149.90	$149.90
Purchase #6	$29.25	9.809%	$32.1191	$32.12	$32.10	$32.10
Purchase #7	$18.72	9.181%	$20.4387	$20.44	$20.45	$20.40
7 purchase totals =	$878.80		$947.4158	$947.42	$947.45	$947.40