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	$114.29	3.419%	$118.1976	$118.20	$118.20	$118.20
Purchase #2	$49.54	10.624%	$54.8031	$54.80	$54.80	$54.80
Purchase #3	$237.81	7.333%	$255.2486	$255.25	$255.25	$255.20
Purchase #4	$151.88	6.152%	$161.2237	$161.22	$161.20	$161.20
Purchase #5	$75.76	13.408%	$85.9179	$85.92	$85.90	$85.90
Purchase #6	$113.27	6.227%	$120.3233	$120.32	$120.30	$120.30
Purchase #7	$49.29	12.798%	$55.5981	$55.60	$55.60	$55.60
7 purchase totals =	$791.84		$851.3123	$851.31	$851.25	$851.20