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	$224.73	6.238%	$238.7487	$238.75	$238.75	$238.70
Purchase #2	$136.88	11.807%	$153.0414	$153.04	$153.05	$153.00
Purchase #3	$179.66	4.568%	$187.8669	$187.87	$187.85	$187.90
Purchase #4	$44.84	11.220%	$49.871	$49.87	$49.85	$49.90
Purchase #5	$85.59	5.318%	$90.1417	$90.14	$90.15	$90.10
Purchase #6	$245.37	11.206%	$272.8662	$272.87	$272.85	$272.90
Purchase #7	$204.86	12.229%	$229.9123	$229.91	$229.90	$229.90
7 purchase totals =	$1,121.93		$1,222.4482	$1,222.45	$1,222.40	$1,222.40