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	$54.64	13.429%	$61.9776	$61.98	$62.00	$62.00
Purchase #2	$165.90	6.412%	$176.5375	$176.54	$176.55	$176.50
Purchase #3	$116.76	10.154%	$128.6158	$128.62	$128.60	$128.60
Purchase #4	$89.57	5.705%	$94.68	$94.68	$94.70	$94.70
Purchase #5	$85.75	13.838%	$97.6161	$97.62	$97.60	$97.60
Purchase #6	$71.42	10.502%	$78.9205	$78.92	$78.90	$78.90
Purchase #7	$27.25	8.498%	$29.5657	$29.57	$29.55	$29.60
7 purchase totals =	$611.29		$667.9132	$667.93	$667.90	$667.90