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	$65.79	5.695%	$69.5367	$69.54	$69.55	$69.50
Purchase #2	$164.47	5.479%	$173.4813	$173.48	$173.50	$173.50
Purchase #3	$97.84	13.412%	$110.9623	$110.96	$110.95	$111.00
Purchase #4	$83.84	6.495%	$89.2854	$89.29	$89.30	$89.30
Purchase #5	$175.82	8.646%	$191.0214	$191.02	$191.00	$191.00
Purchase #6	$82.78	4.856%	$86.7998	$86.80	$86.80	$86.80
Purchase #7	$209.79	13.616%	$238.355	$238.36	$238.35	$238.40
7 purchase totals =	$880.33		$959.4419	$959.45	$959.45	$959.50