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	$173.81	5.582%	$183.5121	$183.51	$183.50	$183.50
Purchase #2	$113.73	10.718%	$125.9196	$125.92	$125.90	$125.90
Purchase #3	$17.33	4.622%	$18.131	$18.13	$18.15	$18.10
Purchase #4	$113.52	8.476%	$123.142	$123.14	$123.15	$123.10
Purchase #5	$25.47	13.553%	$28.9219	$28.92	$28.90	$28.90
Purchase #6	$21.28	3.843%	$22.0978	$22.10	$22.10	$22.10
Purchase #7	$54.59	11.843%	$61.0551	$61.06	$61.05	$61.10
7 purchase totals =	$519.73		$562.7795	$562.78	$562.75	$562.70