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	$159.78	3.812%	$165.8708	$165.87	$165.85	$165.90
Purchase #2	$127.94	7.494%	$137.5278	$137.53	$137.55	$137.50
Purchase #3	$222.41	5.118%	$233.7929	$233.79	$233.80	$233.80
Purchase #4	$196.73	9.176%	$214.7819	$214.78	$214.80	$214.80
Purchase #5	$89.26	6.791%	$95.3216	$95.32	$95.30	$95.30
Purchase #6	$21.82	7.780%	$23.5176	$23.52	$23.50	$23.50
Purchase #7	$6.53	12.328%	$7.335	$7.34	$7.35	$7.30
7 purchase totals =	$824.47		$878.1476	$878.15	$878.15	$878.10