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	$223.75	7.417%	$240.3455	$240.35	$240.35	$240.30
Purchase #2	$103.67	7.865%	$111.8236	$111.82	$111.80	$111.80
Purchase #3	$34.62	4.781%	$36.2752	$36.28	$36.30	$36.30
Purchase #4	$87.85	12.798%	$99.093	$99.09	$99.10	$99.10
Purchase #5	$111.55	11.277%	$124.1295	$124.13	$124.15	$124.10
Purchase #6	$12.98	5.835%	$13.7374	$13.74	$13.75	$13.70
Purchase #7	$19.33	12.868%	$21.8174	$21.82	$21.80	$21.80
7 purchase totals =	$593.75		$647.2216	$647.23	$647.25	$647.10