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	$202.30	13.247%	$229.0987	$229.10	$229.10	$229.10
Purchase #2	$37.72	7.211%	$40.44	$40.44	$40.45	$40.40
Purchase #3	$76.46	11.735%	$85.4326	$85.43	$85.45	$85.40
Purchase #4	$146.82	10.447%	$162.1583	$162.16	$162.15	$162.20
Purchase #5	$95.37	5.754%	$100.8576	$100.86	$100.85	$100.90
Purchase #6	$56.45	11.529%	$62.9581	$62.96	$62.95	$63.00
Purchase #7	$231.63	13.478%	$262.8491	$262.85	$262.85	$262.80
7 purchase totals =	$846.75		$943.7944	$943.80	$943.80	$943.80