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	$63.49	12.178%	$71.2218	$71.22	$71.20	$71.20
Purchase #2	$171.33	8.766%	$186.3488	$186.35	$186.35	$186.30
Purchase #3	$149.78	8.461%	$162.4529	$162.45	$162.45	$162.50
Purchase #4	$37.42	13.270%	$42.3856	$42.39	$42.40	$42.40
Purchase #5	$57.39	11.478%	$63.9772	$63.98	$64.00	$64.00
Purchase #6	$220.87	5.610%	$233.2608	$233.26	$233.25	$233.30
Purchase #7	$65.29	7.419%	$70.1339	$70.13	$70.15	$70.10
7 purchase totals =	$765.57		$829.7810	$829.78	$829.80	$829.80