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	$183.34	10.229%	$202.0938	$202.09	$202.10	$202.10
Purchase #2	$95.48	10.368%	$105.3794	$105.38	$105.40	$105.40
Purchase #3	$222.95	4.797%	$233.6449	$233.64	$233.65	$233.60
Purchase #4	$183.41	5.203%	$192.9528	$192.95	$192.95	$193.00
Purchase #5	$116.57	10.336%	$128.6187	$128.62	$128.60	$128.60
Purchase #6	$79.85	13.782%	$90.8549	$90.85	$90.85	$90.90
Purchase #7	$25.78	9.570%	$28.2471	$28.25	$28.25	$28.20
7 purchase totals =	$907.38		$981.7916	$981.78	$981.80	$981.80