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	$45.72	11.140%	$50.8132	$50.81	$50.80	$50.80
Purchase #2	$90.98	6.328%	$96.7372	$96.74	$96.75	$96.70
Purchase #3	$109.39	8.390%	$118.5678	$118.57	$118.55	$118.60
Purchase #4	$41.60	8.567%	$45.1639	$45.16	$45.15	$45.20
Purchase #5	$248.41	12.556%	$279.6004	$279.60	$279.60	$279.60
Purchase #6	$108.70	4.829%	$113.9491	$113.95	$113.95	$113.90
Purchase #7	$138.95	4.262%	$144.872	$144.87	$144.85	$144.90
7 purchase totals =	$783.75		$849.7036	$849.70	$849.65	$849.70