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	$40.43	12.705%	$45.5666	$45.57	$45.55	$45.60
Purchase #2	$55.73	7.202%	$59.7437	$59.74	$59.75	$59.70
Purchase #3	$250.85	12.526%	$282.2715	$282.27	$282.25	$282.30
Purchase #4	$141.99	4.555%	$148.4576	$148.46	$148.45	$148.50
Purchase #5	$98.38	4.548%	$102.8543	$102.85	$102.85	$102.90
Purchase #6	$65.45	8.660%	$71.118	$71.12	$71.10	$71.10
Purchase #7	$19.45	11.764%	$21.7381	$21.74	$21.75	$21.70
7 purchase totals =	$672.28		$731.7498	$731.75	$731.70	$731.80