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	$33.80	12.112%	$37.8939	$37.89	$37.90	$37.90
Purchase #2	$14.79	7.660%	$15.9229	$15.92	$15.90	$15.90
Purchase #3	$122.98	8.452%	$133.3743	$133.37	$133.35	$133.40
Purchase #4	$118.72	9.835%	$130.3961	$130.40	$130.40	$130.40
Purchase #5	$134.80	13.152%	$152.5289	$152.53	$152.55	$152.50
Purchase #6	$52.84	3.207%	$54.5346	$54.53	$54.55	$54.50
Purchase #7	$59.54	3.192%	$61.4405	$61.44	$61.45	$61.40
7 purchase totals =	$537.47		$586.0912	$586.08	$586.10	$586.00