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	$58.38	13.488%	$66.2543	$66.25	$66.25	$66.30
Purchase #2	$30.95	12.803%	$34.9125	$34.91	$34.90	$34.90
Purchase #3	$80.70	7.334%	$86.6185	$86.62	$86.60	$86.60
Purchase #4	$53.88	10.804%	$59.7012	$59.70	$59.70	$59.70
Purchase #5	$87.61	12.129%	$98.2362	$98.24	$98.25	$98.20
Purchase #6	$11.39	10.672%	$12.6055	$12.61	$12.60	$12.60
Purchase #7	$61.83	4.852%	$64.83	$64.83	$64.85	$64.80
7 purchase totals =	$384.74		$423.1582	$423.16	$423.15	$423.10