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	$47.92	4.818%	$50.2288	$50.23	$50.25	$50.20
Purchase #2	$121.75	12.601%	$137.0917	$137.09	$137.10	$137.10
Purchase #3	$168.42	8.748%	$183.1534	$183.15	$183.15	$183.20
Purchase #4	$101.53	8.741%	$110.4047	$110.40	$110.40	$110.40
Purchase #5	$43.50	7.834%	$46.9078	$46.91	$46.90	$46.90
Purchase #6	$73.54	6.641%	$78.4238	$78.42	$78.40	$78.40
Purchase #7	$31.86	4.733%	$33.3679	$33.37	$33.35	$33.40
7 purchase totals =	$588.52		$639.5781	$639.57	$639.55	$639.60