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	$25.44	10.573%	$28.1298	$28.13	$28.15	$28.10
Purchase #2	$34.84	7.381%	$37.4115	$37.41	$37.40	$37.40
Purchase #3	$82.99	4.204%	$86.4789	$86.48	$86.50	$86.50
Purchase #4	$162.46	5.575%	$171.5171	$171.52	$171.50	$171.50
Purchase #5	$117.97	4.620%	$123.4202	$123.42	$123.40	$123.40
Purchase #6	$99.43	8.197%	$107.5803	$107.58	$107.60	$107.60
Purchase #7	$11.85	8.311%	$12.8349	$12.83	$12.85	$12.80
7 purchase totals =	$534.98		$567.3727	$567.37	$567.40	$567.30