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	$46.85	12.282%	$52.6041	$52.60	$52.60	$52.60
Purchase #2	$83.78	5.457%	$88.3519	$88.35	$88.35	$88.40
Purchase #3	$100.48	10.816%	$111.3479	$111.35	$111.35	$111.30
Purchase #4	$187.25	7.643%	$201.5615	$201.56	$201.55	$201.60
Purchase #5	$206.51	13.173%	$233.7136	$233.71	$233.70	$233.70
Purchase #6	$126.69	13.288%	$143.5246	$143.52	$143.50	$143.50
Purchase #7	$16.80	13.140%	$19.0075	$19.01	$19.00	$19.00
7 purchase totals =	$768.36		$850.1111	$850.10	$850.05	$850.10