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	$171.99	3.505%	$178.0182	$178.02	$178.00	$178.00
Purchase #2	$18.87	9.327%	$20.63	$20.63	$20.65	$20.60
Purchase #3	$157.89	4.857%	$165.5587	$165.56	$165.55	$165.60
Purchase #4	$44.61	9.214%	$48.7204	$48.72	$48.70	$48.70
Purchase #5	$113.80	11.710%	$127.126	$127.13	$127.15	$127.10
Purchase #6	$86.88	9.525%	$95.1553	$95.16	$95.15	$95.20
Purchase #7	$37.33	12.134%	$41.8596	$41.86	$41.85	$41.90
7 purchase totals =	$631.37		$677.0682	$677.08	$677.05	$677.10