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	$80.54	13.357%	$91.2977	$91.30	$91.30	$91.30
Purchase #2	$176.51	7.164%	$189.1552	$189.16	$189.15	$189.20
Purchase #3	$48.56	12.792%	$54.7718	$54.77	$54.75	$54.80
Purchase #4	$176.28	7.120%	$188.8311	$188.83	$188.85	$188.80
Purchase #5	$29.41	13.268%	$33.3121	$33.31	$33.30	$33.30
Purchase #6	$221.46	3.873%	$230.0371	$230.04	$230.05	$230.00
Purchase #7	$136.47	11.516%	$152.1859	$152.19	$152.20	$152.20
7 purchase totals =	$869.23		$939.5909	$939.60	$939.60	$939.60