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	$64.61	4.111%	$67.2661	$67.27	$67.25	$67.30
Purchase #2	$167.72	9.205%	$183.1586	$183.16	$183.15	$183.20
Purchase #3	$127.86	5.571%	$134.9831	$134.98	$135.00	$135.00
Purchase #4	$9.88	9.650%	$10.8334	$10.83	$10.85	$10.80
Purchase #5	$35.49	8.483%	$38.5006	$38.50	$38.50	$38.50
Purchase #6	$36.35	3.195%	$37.5114	$37.51	$37.50	$37.50
Purchase #7	$38.39	12.190%	$43.0697	$43.07	$43.05	$43.10
7 purchase totals =	$480.30		$515.3229	$515.32	$515.30	$515.40