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	$9.91	9.439%	$10.8454	$10.85	$10.85	$10.80
Purchase #2	$85.43	3.340%	$88.2834	$88.28	$88.30	$88.30
Purchase #3	$86.64	13.596%	$98.4196	$98.42	$98.40	$98.40
Purchase #4	$41.25	13.663%	$46.886	$46.89	$46.90	$46.90
Purchase #5	$187.67	9.410%	$205.3297	$205.33	$205.35	$205.30
Purchase #6	$86.55	3.553%	$89.6251	$89.63	$89.65	$89.60
Purchase #7	$47.84	4.634%	$50.0569	$50.06	$50.05	$50.10
7 purchase totals =	$545.29		$589.4461	$589.46	$589.50	$589.40