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	$66.32	6.368%	$70.5433	$70.54	$70.55	$70.50
Purchase #2	$117.54	6.111%	$124.7229	$124.72	$124.70	$124.70
Purchase #3	$90.28	10.457%	$99.7206	$99.72	$99.70	$99.70
Purchase #4	$129.77	10.539%	$143.4465	$143.45	$143.45	$143.40
Purchase #5	$17.54	8.614%	$19.0509	$19.05	$19.05	$19.10
Purchase #6	$138.49	4.238%	$144.3592	$144.36	$144.35	$144.40
Purchase #7	$178.38	5.668%	$188.4906	$188.49	$188.50	$188.50
7 purchase totals =	$738.32		$790.3340	$790.33	$790.30	$790.30