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	$154.42	11.630%	$172.379	$172.38	$172.40	$172.40
Purchase #2	$103.68	4.460%	$108.3041	$108.30	$108.30	$108.30
Purchase #3	$84.51	5.371%	$89.049	$89.05	$89.05	$89.00
Purchase #4	$30.53	3.338%	$31.5491	$31.55	$31.55	$31.50
Purchase #5	$28.46	12.613%	$32.0497	$32.05	$32.05	$32.00
Purchase #6	$238.95	5.416%	$251.8915	$251.89	$251.90	$251.90
Purchase #7	$134.82	3.718%	$139.8326	$139.83	$139.85	$139.80
7 purchase totals =	$775.37		$825.0550	$825.05	$825.10	$824.90