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	$229.56	13.874%	$261.4092	$261.41	$261.40	$261.40
Purchase #2	$87.99	9.482%	$96.3332	$96.33	$96.35	$96.30
Purchase #3	$215.79	11.799%	$241.2511	$241.25	$241.25	$241.30
Purchase #4	$122.46	8.698%	$133.1116	$133.11	$133.10	$133.10
Purchase #5	$100.69	10.368%	$111.1295	$111.13	$111.15	$111.10
Purchase #6	$125.83	13.378%	$142.6635	$142.66	$142.65	$142.70
Purchase #7	$19.64	11.765%	$21.9506	$21.95	$21.95	$22.00
7 purchase totals =	$901.96		$1,007.8487	$1,007.84	$1,007.85	$1,007.90