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	$9.55	5.475%	$10.0729	$10.07	$10.05	$10.10
Purchase #2	$248.94	11.699%	$278.0635	$278.06	$278.05	$278.10
Purchase #3	$128.27	8.378%	$139.0165	$139.02	$139.00	$139.00
Purchase #4	$98.34	3.448%	$101.7308	$101.73	$101.75	$101.70
Purchase #5	$227.85	11.262%	$253.5105	$253.51	$253.50	$253.50
Purchase #6	$83.31	5.760%	$88.1087	$88.11	$88.10	$88.10
Purchase #7	$89.26	12.623%	$100.5273	$100.53	$100.55	$100.50
7 purchase totals =	$885.52		$971.0302	$971.03	$971.00	$971.00