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	$38.56	11.144%	$42.8571	$42.86	$42.85	$42.90
Purchase #2	$124.26	4.773%	$130.1909	$130.19	$130.20	$130.20
Purchase #3	$48.49	5.326%	$51.0726	$51.07	$51.05	$51.10
Purchase #4	$20.50	13.521%	$23.2718	$23.27	$23.25	$23.30
Purchase #5	$45.80	3.778%	$47.5303	$47.53	$47.55	$47.50
Purchase #6	$145.69	7.227%	$156.219	$156.22	$156.20	$156.20
Purchase #7	$51.88	13.870%	$59.0758	$59.08	$59.10	$59.10
7 purchase totals =	$475.18		$510.2175	$510.22	$510.20	$510.30