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	$241.30	12.560%	$271.6073	$271.61	$271.60	$271.60
Purchase #2	$56.27	9.573%	$61.6567	$61.66	$61.65	$61.70
Purchase #3	$40.60	10.529%	$44.8748	$44.87	$44.85	$44.90
Purchase #4	$7.91	13.118%	$8.9476	$8.95	$8.95	$8.90
Purchase #5	$94.50	3.324%	$97.6412	$97.64	$97.65	$97.60
Purchase #6	$76.32	3.207%	$78.7676	$78.77	$78.75	$78.80
Purchase #7	$111.33	7.662%	$119.8601	$119.86	$119.85	$119.90
7 purchase totals =	$628.23		$683.3553	$683.36	$683.30	$683.40