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	$134.73	4.121%	$140.2822	$140.28	$140.30	$140.30
Purchase #2	$231.32	13.521%	$262.5968	$262.60	$262.60	$262.60
Purchase #3	$178.32	7.234%	$191.2197	$191.22	$191.20	$191.20
Purchase #4	$164.70	8.761%	$179.1294	$179.13	$179.15	$179.10
Purchase #5	$248.30	7.103%	$265.9367	$265.94	$265.95	$265.90
Purchase #6	$45.54	12.837%	$51.386	$51.39	$51.40	$51.40
Purchase #7	$167.39	13.723%	$190.3609	$190.36	$190.35	$190.40
7 purchase totals =	$1,170.30		$1,280.9117	$1,280.92	$1,280.95	$1,280.90