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	$47.45	4.823%	$49.7385	$49.74	$49.75	$49.70
Purchase #2	$134.64	5.722%	$142.3441	$142.34	$142.35	$142.30
Purchase #3	$112.56	3.300%	$116.2745	$116.27	$116.25	$116.30
Purchase #4	$85.89	9.256%	$93.84	$93.84	$93.85	$93.80
Purchase #5	$74.77	10.650%	$82.733	$82.73	$82.75	$82.70
Purchase #6	$233.79	3.256%	$241.4022	$241.40	$241.40	$241.40
Purchase #7	$56.70	5.673%	$59.9166	$59.92	$59.90	$59.90
7 purchase totals =	$745.80		$786.2489	$786.24	$786.25	$786.10