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	$42.76	10.595%	$47.2904	$47.29	$47.30	$47.30
Purchase #2	$176.95	7.779%	$190.7149	$190.71	$190.70	$190.70
Purchase #3	$29.28	9.757%	$32.1368	$32.14	$32.15	$32.10
Purchase #4	$210.92	3.649%	$218.6165	$218.62	$218.60	$218.60
Purchase #5	$136.46	11.865%	$152.651	$152.65	$152.65	$152.70
Purchase #6	$14.50	13.309%	$16.4298	$16.43	$16.45	$16.40
Purchase #7	$77.51	6.349%	$82.4311	$82.43	$82.45	$82.40
7 purchase totals =	$688.38		$740.2705	$740.27	$740.30	$740.20