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	$18.28	5.482%	$19.2821	$19.28	$19.30	$19.30
Purchase #2	$170.63	11.342%	$189.9829	$189.98	$190.00	$190.00
Purchase #3	$155.87	10.392%	$172.068	$172.07	$172.05	$172.10
Purchase #4	$87.38	6.339%	$92.919	$92.92	$92.90	$92.90
Purchase #5	$36.43	12.227%	$40.8843	$40.88	$40.90	$40.90
Purchase #6	$61.70	6.227%	$65.5421	$65.54	$65.55	$65.50
Purchase #7	$11.83	9.514%	$12.9555	$12.96	$12.95	$13.00
7 purchase totals =	$542.12		$593.6339	$593.63	$593.65	$593.70