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	$62.71	7.733%	$67.5594	$67.56	$67.55	$67.60
Purchase #2	$72.39	8.848%	$78.7951	$78.80	$78.80	$78.80
Purchase #3	$105.28	8.568%	$114.3004	$114.30	$114.30	$114.30
Purchase #4	$20.47	11.502%	$22.8245	$22.82	$22.80	$22.80
Purchase #5	$91.29	12.401%	$102.6109	$102.61	$102.60	$102.60
Purchase #6	$224.71	4.791%	$235.4759	$235.48	$235.50	$235.50
Purchase #7	$150.58	11.174%	$167.4058	$167.41	$167.40	$167.40
7 purchase totals =	$727.43		$788.9720	$788.98	$788.95	$789.00