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	$190.50	13.615%	$216.4366	$216.44	$216.45	$216.40
Purchase #2	$97.78	11.551%	$109.0746	$109.07	$109.05	$109.10
Purchase #3	$148.80	10.631%	$164.6189	$164.62	$164.60	$164.60
Purchase #4	$171.69	8.695%	$186.6184	$186.62	$186.60	$186.60
Purchase #5	$56.75	5.420%	$59.8259	$59.83	$59.85	$59.80
Purchase #6	$62.30	7.108%	$66.7283	$66.73	$66.75	$66.70
Purchase #7	$48.60	10.424%	$53.6661	$53.67	$53.65	$53.70
7 purchase totals =	$776.42		$856.9688	$856.98	$856.95	$856.90