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	$218.60	9.228%	$238.7724	$238.77	$238.75	$238.80
Purchase #2	$102.67	6.728%	$109.5776	$109.58	$109.60	$109.60
Purchase #3	$139.54	6.191%	$148.1789	$148.18	$148.20	$148.20
Purchase #4	$121.43	7.377%	$130.3879	$130.39	$130.40	$130.40
Purchase #5	$53.86	10.659%	$59.6009	$59.60	$59.60	$59.60
Purchase #6	$53.86	12.670%	$60.6841	$60.68	$60.70	$60.70
Purchase #7	$101.83	7.510%	$109.4774	$109.48	$109.50	$109.50
7 purchase totals =	$791.79		$856.6792	$856.68	$856.75	$856.80