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	$121.92	4.243%	$127.0931	$127.09	$127.10	$127.10
Purchase #2	$142.47	12.116%	$159.7317	$159.73	$159.75	$159.70
Purchase #3	$230.85	8.793%	$251.1486	$251.15	$251.15	$251.10
Purchase #4	$55.70	7.132%	$59.6725	$59.67	$59.65	$59.70
Purchase #5	$28.83	13.308%	$32.6667	$32.67	$32.65	$32.70
Purchase #6	$185.90	10.824%	$206.0218	$206.02	$206.00	$206.00
Purchase #7	$84.86	6.740%	$90.5796	$90.58	$90.60	$90.60
7 purchase totals =	$850.53		$926.9140	$926.91	$926.90	$926.90