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	$92.87	8.227%	$100.5104	$100.51	$100.50	$100.50
Purchase #2	$196.33	7.130%	$210.3283	$210.33	$210.35	$210.30
Purchase #3	$26.95	8.371%	$29.206	$29.21	$29.20	$29.20
Purchase #4	$62.66	13.112%	$70.876	$70.88	$70.90	$70.90
Purchase #5	$17.33	3.407%	$17.9204	$17.92	$17.90	$17.90
Purchase #6	$97.45	7.670%	$104.9244	$104.92	$104.90	$104.90
Purchase #7	$39.81	6.852%	$42.5378	$42.54	$42.55	$42.50
7 purchase totals =	$533.40		$576.3033	$576.31	$576.30	$576.20