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	$22.86	8.631%	$24.833	$24.83	$24.85	$24.80
Purchase #2	$105.41	6.755%	$112.5304	$112.53	$112.55	$112.50
Purchase #3	$82.49	12.194%	$92.5488	$92.55	$92.55	$92.50
Purchase #4	$36.30	10.128%	$39.9765	$39.98	$40.00	$40.00
Purchase #5	$133.69	7.417%	$143.6058	$143.61	$143.60	$143.60
Purchase #6	$166.88	3.285%	$172.362	$172.36	$172.35	$172.40
Purchase #7	$93.77	3.244%	$96.8119	$96.81	$96.80	$96.80
7 purchase totals =	$641.40		$682.6684	$682.67	$682.70	$682.60