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	$95.70	4.751%	$100.2467	$100.25	$100.25	$100.20
Purchase #2	$189.90	8.645%	$206.3169	$206.32	$206.30	$206.30
Purchase #3	$35.41	8.733%	$38.5024	$38.50	$38.50	$38.50
Purchase #4	$144.80	13.599%	$164.4914	$164.49	$164.50	$164.50
Purchase #5	$127.32	11.401%	$141.8358	$141.84	$141.85	$141.80
Purchase #6	$27.90	5.183%	$29.3461	$29.35	$29.35	$29.30
Purchase #7	$61.39	10.483%	$67.8255	$67.83	$67.85	$67.80
7 purchase totals =	$682.42		$748.5648	$748.58	$748.60	$748.40