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	$224.89	13.747%	$255.8056	$255.81	$255.80	$255.80
Purchase #2	$233.58	8.730%	$253.9715	$253.97	$253.95	$254.00
Purchase #3	$124.55	10.740%	$137.9267	$137.93	$137.95	$137.90
Purchase #4	$121.82	12.495%	$137.0414	$137.04	$137.05	$137.00
Purchase #5	$58.37	12.507%	$65.6703	$65.67	$65.65	$65.70
Purchase #6	$86.43	12.153%	$96.9338	$96.93	$96.95	$96.90
Purchase #7	$169.65	6.188%	$180.1479	$180.15	$180.15	$180.10
7 purchase totals =	$1,019.29		$1,127.4972	$1,127.50	$1,127.50	$1,127.40