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	$125.97	11.612%	$140.5976	$140.60	$140.60	$140.60
Purchase #2	$213.75	13.477%	$242.5571	$242.56	$242.55	$242.60
Purchase #3	$85.94	4.293%	$89.6294	$89.63	$89.65	$89.60
Purchase #4	$239.36	6.405%	$254.691	$254.69	$254.70	$254.70
Purchase #5	$154.44	12.548%	$173.8191	$173.82	$173.80	$173.80
Purchase #6	$110.45	12.133%	$123.8509	$123.85	$123.85	$123.90
Purchase #7	$236.25	7.780%	$254.6303	$254.63	$254.65	$254.60
7 purchase totals =	$1,166.16		$1,279.7754	$1,279.78	$1,279.80	$1,279.80