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	$50.93	6.420%	$54.1997	$54.20	$54.20	$54.20
Purchase #2	$63.32	9.145%	$69.1106	$69.11	$69.10	$69.10
Purchase #3	$40.28	11.286%	$44.826	$44.83	$44.85	$44.80
Purchase #4	$82.45	7.480%	$88.6173	$88.62	$88.60	$88.60
Purchase #5	$138.57	8.766%	$150.717	$150.72	$150.70	$150.70
Purchase #6	$48.59	9.630%	$53.2692	$53.27	$53.25	$53.30
Purchase #7	$222.55	10.437%	$245.7775	$245.78	$245.80	$245.80
7 purchase totals =	$646.69		$706.5173	$706.53	$706.50	$706.50