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	$168.34	13.419%	$190.9295	$190.93	$190.95	$190.90
Purchase #2	$95.41	10.590%	$105.5139	$105.51	$105.50	$105.50
Purchase #3	$74.96	6.684%	$79.9703	$79.97	$79.95	$80.00
Purchase #4	$40.83	11.806%	$45.6504	$45.65	$45.65	$45.70
Purchase #5	$139.57	5.713%	$147.5436	$147.54	$147.55	$147.50
Purchase #6	$96.60	13.740%	$109.8728	$109.87	$109.85	$109.90
Purchase #7	$142.77	12.115%	$160.0666	$160.07	$160.05	$160.10
7 purchase totals =	$758.48		$839.5471	$839.54	$839.50	$839.60