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	$157.88	13.256%	$178.8086	$178.81	$178.80	$178.80
Purchase #2	$148.38	13.801%	$168.8579	$168.86	$168.85	$168.90
Purchase #3	$245.96	10.472%	$271.7169	$271.72	$271.70	$271.70
Purchase #4	$17.81	10.715%	$19.7183	$19.72	$19.70	$19.70
Purchase #5	$7.35	6.499%	$7.8277	$7.83	$7.85	$7.80
Purchase #6	$50.58	4.239%	$52.7241	$52.72	$52.70	$52.70
Purchase #7	$153.98	12.207%	$172.7763	$172.78	$172.80	$172.80
7 purchase totals =	$781.94		$872.4298	$872.44	$872.40	$872.40