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	$178.82	4.572%	$186.9957	$187.00	$187.00	$187.00
Purchase #2	$157.72	13.301%	$178.6983	$178.70	$178.70	$178.70
Purchase #3	$106.28	4.561%	$111.1274	$111.13	$111.15	$111.10
Purchase #4	$49.59	8.842%	$53.9747	$53.97	$53.95	$54.00
Purchase #5	$42.29	7.526%	$45.4727	$45.47	$45.45	$45.50
Purchase #6	$53.46	3.517%	$55.3402	$55.34	$55.35	$55.30
Purchase #7	$39.98	3.269%	$41.2869	$41.29	$41.30	$41.30
7 purchase totals =	$628.14		$672.8959	$672.90	$672.90	$672.90