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	$19.49	7.478%	$20.9475	$20.95	$20.95	$20.90
Purchase #2	$176.41	13.235%	$199.7579	$199.76	$199.75	$199.80
Purchase #3	$74.30	5.419%	$78.3263	$78.33	$78.35	$78.30
Purchase #4	$43.28	6.277%	$45.9967	$46.00	$46.00	$46.00
Purchase #5	$18.33	10.618%	$20.2763	$20.28	$20.30	$20.30
Purchase #6	$59.38	9.707%	$65.144	$65.14	$65.15	$65.10
Purchase #7	$99.41	7.503%	$106.8687	$106.87	$106.85	$106.90
7 purchase totals =	$490.60		$537.3174	$537.33	$537.35	$537.30