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	$215.35	10.837%	$238.6875	$238.69	$238.70	$238.70
Purchase #2	$40.90	9.128%	$44.6334	$44.63	$44.65	$44.60
Purchase #3	$138.59	5.505%	$146.2194	$146.22	$146.20	$146.20
Purchase #4	$13.27	8.663%	$14.4196	$14.42	$14.40	$14.40
Purchase #5	$110.71	11.116%	$123.0165	$123.02	$123.00	$123.00
Purchase #6	$33.31	13.127%	$37.6826	$37.68	$37.70	$37.70
Purchase #7	$50.38	11.194%	$56.0195	$56.02	$56.00	$56.00
7 purchase totals =	$602.51		$660.6785	$660.68	$660.65	$660.60