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	$48.85	12.305%	$54.861	$54.86	$54.85	$54.90
Purchase #2	$94.87	13.275%	$107.464	$107.46	$107.45	$107.50
Purchase #3	$159.79	8.692%	$173.6789	$173.68	$173.70	$173.70
Purchase #4	$103.73	5.155%	$109.0773	$109.08	$109.10	$109.10
Purchase #5	$142.39	6.830%	$152.1152	$152.12	$152.10	$152.10
Purchase #6	$246.67	3.466%	$255.2196	$255.22	$255.20	$255.20
Purchase #7	$133.98	13.310%	$151.8127	$151.81	$151.80	$151.80
7 purchase totals =	$930.28		$1,004.2287	$1,004.23	$1,004.20	$1,004.30