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	$108.63	6.865%	$116.0874	$116.09	$116.10	$116.10
Purchase #2	$150.41	12.145%	$168.6773	$168.68	$168.70	$168.70
Purchase #3	$170.79	8.860%	$185.922	$185.92	$185.90	$185.90
Purchase #4	$85.26	13.239%	$96.5476	$96.55	$96.55	$96.50
Purchase #5	$83.60	12.784%	$94.2874	$94.29	$94.30	$94.30
Purchase #6	$56.41	5.600%	$59.569	$59.57	$59.55	$59.60
Purchase #7	$60.55	3.750%	$62.8206	$62.82	$62.80	$62.80
7 purchase totals =	$715.65		$783.9113	$783.92	$783.90	$783.90