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	$56.27	4.700%	$58.9147	$58.91	$58.90	$58.90
Purchase #2	$100.94	4.624%	$105.6075	$105.61	$105.60	$105.60
Purchase #3	$144.37	8.716%	$156.9533	$156.95	$156.95	$157.00
Purchase #4	$94.51	10.107%	$104.0621	$104.06	$104.05	$104.10
Purchase #5	$6.27	7.290%	$6.7271	$6.73	$6.75	$6.70
Purchase #6	$36.39	12.370%	$40.8914	$40.89	$40.90	$40.90
Purchase #7	$41.26	9.797%	$45.3022	$45.30	$45.30	$45.30
7 purchase totals =	$480.01		$518.4583	$518.45	$518.45	$518.50