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	$58.70	12.248%	$65.8896	$65.89	$65.90	$65.90
Purchase #2	$58.58	12.592%	$65.9564	$65.96	$65.95	$66.00
Purchase #3	$87.78	12.768%	$98.9878	$98.99	$99.00	$99.00
Purchase #4	$54.70	3.243%	$56.4739	$56.47	$56.45	$56.50
Purchase #5	$109.72	5.645%	$115.9137	$115.91	$115.90	$115.90
Purchase #6	$79.54	3.854%	$82.6055	$82.61	$82.60	$82.60
Purchase #7	$51.76	12.527%	$58.244	$58.24	$58.25	$58.20
7 purchase totals =	$500.78		$544.0709	$544.07	$544.05	$544.10