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	$250.70	5.855%	$265.3785	$265.38	$265.40	$265.40
Purchase #2	$200.49	11.411%	$223.3679	$223.37	$223.35	$223.40
Purchase #3	$24.91	7.588%	$26.8002	$26.80	$26.80	$26.80
Purchase #4	$37.61	6.145%	$39.9211	$39.92	$39.90	$39.90
Purchase #5	$82.85	7.535%	$89.0927	$89.09	$89.10	$89.10
Purchase #6	$58.42	11.585%	$65.188	$65.19	$65.20	$65.20
Purchase #7	$167.91	11.447%	$187.1307	$187.13	$187.15	$187.10
7 purchase totals =	$822.89		$896.8791	$896.88	$896.90	$896.90