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	$153.26	12.368%	$172.2152	$172.22	$172.20	$172.20
Purchase #2	$41.52	11.139%	$46.1449	$46.14	$46.15	$46.10
Purchase #3	$144.80	7.496%	$155.6542	$155.65	$155.65	$155.70
Purchase #4	$106.35	5.820%	$112.5396	$112.54	$112.55	$112.50
Purchase #5	$124.41	8.180%	$134.5867	$134.59	$134.60	$134.60
Purchase #6	$48.34	13.455%	$54.8441	$54.84	$54.85	$54.80
Purchase #7	$166.65	8.559%	$180.9136	$180.91	$180.90	$180.90
7 purchase totals =	$785.33		$856.8983	$856.89	$856.90	$856.80