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	$125.71	10.473%	$138.8756	$138.88	$138.90	$138.90
Purchase #2	$214.84	8.861%	$233.877	$233.88	$233.90	$233.90
Purchase #3	$84.97	5.611%	$89.7377	$89.74	$89.75	$89.70
Purchase #4	$110.79	11.869%	$123.9397	$123.94	$123.95	$123.90
Purchase #5	$55.68	6.205%	$59.1349	$59.13	$59.15	$59.10
Purchase #6	$49.93	9.382%	$54.6144	$54.61	$54.60	$54.60
Purchase #7	$70.98	12.510%	$79.8596	$79.86	$79.85	$79.90
7 purchase totals =	$712.90		$780.0389	$780.04	$780.10	$780.00