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	$141.59	13.345%	$160.4852	$160.49	$160.50	$160.50
Purchase #2	$187.83	6.480%	$200.0014	$200.00	$200.00	$200.00
Purchase #3	$200.27	6.141%	$212.5686	$212.57	$212.55	$212.60
Purchase #4	$84.95	6.809%	$90.7342	$90.73	$90.75	$90.70
Purchase #5	$72.29	9.359%	$79.0556	$79.06	$79.05	$79.10
Purchase #6	$45.71	13.468%	$51.8662	$51.87	$51.85	$51.90
Purchase #7	$121.30	8.348%	$131.4261	$131.43	$131.45	$131.40
7 purchase totals =	$853.94		$926.1373	$926.15	$926.15	$926.20