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	$114.41	5.687%	$120.9165	$120.92	$120.90	$120.90
Purchase #2	$157.98	8.862%	$171.9802	$171.98	$172.00	$172.00
Purchase #3	$113.43	12.732%	$127.8719	$127.87	$127.85	$127.90
Purchase #4	$72.51	4.183%	$75.5431	$75.54	$75.55	$75.50
Purchase #5	$111.79	11.845%	$125.0315	$125.03	$125.05	$125.00
Purchase #6	$184.52	7.771%	$198.859	$198.86	$198.85	$198.90
Purchase #7	$245.83	5.238%	$258.7066	$258.71	$258.70	$258.70
7 purchase totals =	$1,000.47		$1,078.9088	$1,078.91	$1,078.90	$1,078.90