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	$166.55	7.727%	$179.4193	$179.42	$179.40	$179.40
Purchase #2	$238.39	8.293%	$258.1597	$258.16	$258.15	$258.20
Purchase #3	$169.90	4.386%	$177.3518	$177.35	$177.35	$177.40
Purchase #4	$245.67	7.846%	$264.9453	$264.95	$264.95	$264.90
Purchase #5	$127.64	9.166%	$139.3395	$139.34	$139.35	$139.30
Purchase #6	$176.49	7.727%	$190.1274	$190.13	$190.15	$190.10
Purchase #7	$123.50	3.248%	$127.5113	$127.51	$127.50	$127.50
7 purchase totals =	$1,248.14		$1,336.8543	$1,336.86	$1,336.85	$1,336.80