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	$116.93	6.453%	$124.4755	$124.48	$124.50	$124.50
Purchase #2	$94.52	7.337%	$101.4549	$101.45	$101.45	$101.50
Purchase #3	$205.68	9.466%	$225.1497	$225.15	$225.15	$225.10
Purchase #4	$69.70	4.375%	$72.7494	$72.75	$72.75	$72.70
Purchase #5	$180.79	8.566%	$196.2765	$196.28	$196.30	$196.30
Purchase #6	$94.81	9.207%	$103.5392	$103.54	$103.55	$103.50
Purchase #7	$6.29	9.801%	$6.9065	$6.91	$6.90	$6.90
7 purchase totals =	$768.72		$830.5517	$830.56	$830.60	$830.50