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	$163.99	4.157%	$170.8071	$170.81	$170.80	$170.80
Purchase #2	$60.77	7.525%	$65.3429	$65.34	$65.35	$65.30
Purchase #3	$121.73	4.594%	$127.3223	$127.32	$127.30	$127.30
Purchase #4	$89.89	11.795%	$100.4925	$100.49	$100.50	$100.50
Purchase #5	$71.42	5.523%	$75.3645	$75.36	$75.35	$75.40
Purchase #6	$32.93	3.310%	$34.02	$34.02	$34.00	$34.00
Purchase #7	$61.32	10.273%	$67.6194	$67.62	$67.60	$67.60
7 purchase totals =	$602.05		$640.9687	$640.96	$640.90	$640.90