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	$53.26	5.350%	$56.1094	$56.11	$56.10	$56.10
Purchase #2	$181.78	4.631%	$190.1982	$190.20	$190.20	$190.20
Purchase #3	$24.78	6.343%	$26.3518	$26.35	$26.35	$26.40
Purchase #4	$239.65	6.824%	$256.0037	$256.00	$256.00	$256.00
Purchase #5	$6.40	11.335%	$7.1254	$7.13	$7.15	$7.10
Purchase #6	$53.33	12.215%	$59.8443	$59.84	$59.85	$59.80
Purchase #7	$40.81	10.505%	$45.0971	$45.10	$45.10	$45.10
7 purchase totals =	$600.01		$640.7299	$640.73	$640.75	$640.70