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	$249.71	13.151%	$282.5494	$282.55	$282.55	$282.50
Purchase #2	$125.50	4.149%	$130.707	$130.71	$130.70	$130.70
Purchase #3	$171.82	4.778%	$180.0296	$180.03	$180.05	$180.00
Purchase #4	$83.27	11.309%	$92.687	$92.69	$92.70	$92.70
Purchase #5	$61.89	8.195%	$66.9619	$66.96	$66.95	$67.00
Purchase #6	$232.42	3.318%	$240.1317	$240.13	$240.15	$240.10
Purchase #7	$71.42	9.256%	$78.0306	$78.03	$78.05	$78.00
7 purchase totals =	$996.03		$1,071.0972	$1,071.10	$1,071.15	$1,071.00