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	$127.99	5.840%	$135.4646	$135.46	$135.45	$135.50
Purchase #2	$103.45	7.651%	$111.365	$111.37	$111.35	$111.40
Purchase #3	$134.66	9.363%	$147.2682	$147.27	$147.25	$147.30
Purchase #4	$134.97	5.331%	$142.1653	$142.17	$142.15	$142.20
Purchase #5	$144.48	13.684%	$164.2506	$164.25	$164.25	$164.30
Purchase #6	$104.41	8.231%	$113.004	$113.00	$113.00	$113.00
Purchase #7	$76.54	13.174%	$86.6234	$86.62	$86.60	$86.60
7 purchase totals =	$826.50		$900.1411	$900.14	$900.05	$900.30