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	$229.86	11.197%	$255.5974	$255.60	$255.60	$255.60
Purchase #2	$129.90	5.196%	$136.6496	$136.65	$136.65	$136.60
Purchase #3	$168.74	11.763%	$188.5889	$188.59	$188.60	$188.60
Purchase #4	$152.60	13.350%	$172.9721	$172.97	$172.95	$173.00
Purchase #5	$126.53	7.790%	$136.3867	$136.39	$136.40	$136.40
Purchase #6	$168.98	5.479%	$178.2384	$178.24	$178.25	$178.20
Purchase #7	$171.57	4.257%	$178.8737	$178.87	$178.85	$178.90
7 purchase totals =	$1,148.18		$1,247.3068	$1,247.31	$1,247.30	$1,247.30