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	$30.25	13.704%	$34.3955	$34.40	$34.40	$34.40
Purchase #2	$121.78	12.463%	$136.9574	$136.96	$136.95	$137.00
Purchase #3	$190.89	10.852%	$211.6054	$211.61	$211.60	$211.60
Purchase #4	$60.25	11.269%	$67.0396	$67.04	$67.05	$67.00
Purchase #5	$76.52	11.395%	$85.2395	$85.24	$85.25	$85.20
Purchase #6	$95.86	10.462%	$105.8889	$105.89	$105.90	$105.90
Purchase #7	$110.96	8.106%	$119.9544	$119.95	$119.95	$120.00
7 purchase totals =	$686.51		$761.0807	$761.09	$761.10	$761.10