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	$85.47	4.489%	$89.3067	$89.31	$89.30	$89.30
Purchase #2	$66.71	8.692%	$72.5084	$72.51	$72.50	$72.50
Purchase #3	$249.43	8.150%	$269.7585	$269.76	$269.75	$269.80
Purchase #4	$173.77	5.531%	$183.3812	$183.38	$183.40	$183.40
Purchase #5	$186.63	11.290%	$207.7005	$207.70	$207.70	$207.70
Purchase #6	$204.75	4.188%	$213.3249	$213.32	$213.30	$213.30
Purchase #7	$137.46	7.773%	$148.1448	$148.14	$148.15	$148.10
7 purchase totals =	$1,104.22		$1,184.1250	$1,184.12	$1,184.10	$1,184.10