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	$79.75	7.589%	$85.8022	$85.80	$85.80	$85.80
Purchase #2	$214.92	11.792%	$240.2634	$240.26	$240.25	$240.30
Purchase #3	$206.25	5.778%	$218.1671	$218.17	$218.15	$218.20
Purchase #4	$37.95	12.683%	$42.7632	$42.76	$42.75	$42.80
Purchase #5	$107.36	4.181%	$111.8487	$111.85	$111.85	$111.80
Purchase #6	$152.87	3.711%	$158.543	$158.54	$158.55	$158.50
Purchase #7	$202.39	10.145%	$222.9225	$222.92	$222.90	$222.90
7 purchase totals =	$1,001.49		$1,080.3101	$1,080.30	$1,080.25	$1,080.30