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	$148.89	13.228%	$168.5852	$168.59	$168.60	$168.60
Purchase #2	$230.79	10.477%	$254.9699	$254.97	$254.95	$255.00
Purchase #3	$221.49	7.749%	$238.6533	$238.65	$238.65	$238.70
Purchase #4	$194.54	4.545%	$203.3818	$203.38	$203.40	$203.40
Purchase #5	$110.60	11.769%	$123.6165	$123.62	$123.60	$123.60
Purchase #6	$212.85	13.448%	$241.4741	$241.47	$241.45	$241.50
Purchase #7	$88.63	13.720%	$100.79	$100.79	$100.80	$100.80
7 purchase totals =	$1,207.79		$1,331.4708	$1,331.47	$1,331.45	$1,331.60