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	$98.45	5.398%	$103.7643	$103.76	$103.75	$103.80
Purchase #2	$171.82	3.459%	$177.7633	$177.76	$177.75	$177.80
Purchase #3	$49.75	8.345%	$53.9016	$53.90	$53.90	$53.90
Purchase #4	$168.90	3.256%	$174.3994	$174.40	$174.40	$174.40
Purchase #5	$65.89	8.697%	$71.6205	$71.62	$71.60	$71.60
Purchase #6	$32.27	7.111%	$34.5647	$34.56	$34.55	$34.60
Purchase #7	$22.50	5.360%	$23.706	$23.71	$23.70	$23.70
7 purchase totals =	$609.58		$639.7198	$639.71	$639.65	$639.80