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	$58.27	10.761%	$64.5404	$64.54	$64.55	$64.50
Purchase #2	$178.75	6.536%	$190.4331	$190.43	$190.45	$190.40
Purchase #3	$64.87	8.153%	$70.1589	$70.16	$70.15	$70.20
Purchase #4	$180.61	12.538%	$203.2549	$203.25	$203.25	$203.30
Purchase #5	$131.93	10.397%	$145.6468	$145.65	$145.65	$145.60
Purchase #6	$32.72	3.166%	$33.7559	$33.76	$33.75	$33.80
Purchase #7	$89.83	7.844%	$96.8763	$96.88	$96.90	$96.90
7 purchase totals =	$736.98		$804.6663	$804.67	$804.70	$804.70