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	$37.56	5.652%	$39.6829	$39.68	$39.70	$39.70
Purchase #2	$56.52	3.426%	$58.4564	$58.46	$58.45	$58.50
Purchase #3	$40.41	4.651%	$42.2895	$42.29	$42.30	$42.30
Purchase #4	$124.30	12.758%	$140.1582	$140.16	$140.15	$140.20
Purchase #5	$108.93	9.582%	$119.3677	$119.37	$119.35	$119.40
Purchase #6	$210.50	11.361%	$234.4149	$234.41	$234.40	$234.40
Purchase #7	$11.54	11.803%	$12.9021	$12.90	$12.90	$12.90
7 purchase totals =	$589.76		$647.2717	$647.27	$647.25	$647.40