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	$38.91	3.609%	$40.3143	$40.31	$40.30	$40.30
Purchase #2	$229.76	5.103%	$241.4847	$241.48	$241.50	$241.50
Purchase #3	$219.44	4.333%	$228.9483	$228.95	$228.95	$228.90
Purchase #4	$129.61	9.532%	$141.9644	$141.96	$141.95	$142.00
Purchase #5	$249.97	11.567%	$278.884	$278.88	$278.90	$278.90
Purchase #6	$31.68	8.450%	$34.357	$34.36	$34.35	$34.40
Purchase #7	$11.40	10.708%	$12.6207	$12.62	$12.60	$12.60
7 purchase totals =	$910.77		$978.5734	$978.56	$978.55	$978.60