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	$48.90	5.453%	$51.5665	$51.57	$51.55	$51.60
Purchase #2	$150.73	11.764%	$168.4619	$168.46	$168.45	$168.50
Purchase #3	$62.93	13.741%	$71.5772	$71.58	$71.60	$71.60
Purchase #4	$34.94	12.862%	$39.434	$39.43	$39.45	$39.40
Purchase #5	$52.47	13.728%	$59.6731	$59.67	$59.65	$59.70
Purchase #6	$19.35	12.186%	$21.708	$21.71	$21.70	$21.70
Purchase #7	$52.40	13.160%	$59.2958	$59.30	$59.30	$59.30
7 purchase totals =	$421.72		$471.7165	$471.72	$471.70	$471.80