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	$30.83	12.633%	$34.7248	$34.72	$34.70	$34.70
Purchase #2	$82.57	9.573%	$90.4744	$90.47	$90.45	$90.50
Purchase #3	$209.73	13.685%	$238.4316	$238.43	$238.45	$238.40
Purchase #4	$174.95	12.200%	$196.2939	$196.29	$196.30	$196.30
Purchase #5	$237.36	4.795%	$248.7414	$248.74	$248.75	$248.70
Purchase #6	$196.27	6.367%	$208.7665	$208.77	$208.75	$208.80
Purchase #7	$212.50	13.212%	$240.5755	$240.58	$240.60	$240.60
7 purchase totals =	$1,144.21		$1,258.0081	$1,258.00	$1,258.00	$1,258.00