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	$144.37	5.853%	$152.82	$152.82	$152.80	$152.80
Purchase #2	$243.89	13.406%	$276.5859	$276.59	$276.60	$276.60
Purchase #3	$132.92	4.839%	$139.352	$139.35	$139.35	$139.40
Purchase #4	$163.54	9.109%	$178.4369	$178.44	$178.45	$178.40
Purchase #5	$129.40	12.872%	$146.0564	$146.06	$146.05	$146.10
Purchase #6	$174.56	10.435%	$192.7753	$192.78	$192.80	$192.80
Purchase #7	$200.64	9.159%	$219.0166	$219.02	$219.00	$219.00
7 purchase totals =	$1,189.32		$1,305.0431	$1,305.06	$1,305.05	$1,305.10