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	$232.70	12.280%	$261.2756	$261.28	$261.30	$261.30
Purchase #2	$77.86	5.728%	$82.3198	$82.32	$82.30	$82.30
Purchase #3	$234.63	10.209%	$258.5834	$258.58	$258.60	$258.60
Purchase #4	$52.95	8.226%	$57.3057	$57.31	$57.30	$57.30
Purchase #5	$84.52	8.152%	$91.4101	$91.41	$91.40	$91.40
Purchase #6	$57.50	7.144%	$61.6078	$61.61	$61.60	$61.60
Purchase #7	$249.38	4.133%	$259.6869	$259.69	$259.70	$259.70
7 purchase totals =	$989.54		$1,072.1893	$1,072.20	$1,072.20	$1,072.20