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	$108.66	3.620%	$112.5935	$112.59	$112.60	$112.60
Purchase #2	$205.91	8.585%	$223.5874	$223.59	$223.60	$223.60
Purchase #3	$37.42	10.281%	$41.2672	$41.27	$41.25	$41.30
Purchase #4	$149.79	5.707%	$158.3385	$158.34	$158.35	$158.30
Purchase #5	$33.63	12.428%	$37.8095	$37.81	$37.80	$37.80
Purchase #6	$24.62	3.731%	$25.5386	$25.54	$25.55	$25.50
Purchase #7	$82.79	10.531%	$91.5086	$91.51	$91.50	$91.50
7 purchase totals =	$642.82		$690.6433	$690.65	$690.65	$690.60