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	$23.45	5.426%	$24.7224	$24.72	$24.70	$24.70
Purchase #2	$124.76	5.312%	$131.3873	$131.39	$131.40	$131.40
Purchase #3	$51.59	4.236%	$53.7754	$53.78	$53.80	$53.80
Purchase #4	$116.46	10.115%	$128.2399	$128.24	$128.25	$128.20
Purchase #5	$242.43	4.493%	$253.3224	$253.32	$253.30	$253.30
Purchase #6	$204.95	13.741%	$233.1122	$233.11	$233.10	$233.10
Purchase #7	$177.79	9.802%	$195.217	$195.22	$195.20	$195.20
7 purchase totals =	$941.43		$1,019.7766	$1,019.78	$1,019.75	$1,019.70