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	$20.89	13.185%	$23.6443	$23.64	$23.65	$23.60
Purchase #2	$144.34	8.687%	$156.8788	$156.88	$156.90	$156.90
Purchase #3	$159.59	13.573%	$181.2512	$181.25	$181.25	$181.30
Purchase #4	$210.78	5.593%	$222.5689	$222.57	$222.55	$222.60
Purchase #5	$198.68	3.806%	$206.2418	$206.24	$206.25	$206.20
Purchase #6	$6.42	5.696%	$6.7857	$6.79	$6.80	$6.80
Purchase #7	$207.96	6.753%	$222.0035	$222.00	$222.00	$222.00
7 purchase totals =	$948.66		$1,019.3742	$1,019.37	$1,019.40	$1,019.40