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	$84.76	5.677%	$89.5718	$89.57	$89.55	$89.60
Purchase #2	$67.77	13.188%	$76.7075	$76.71	$76.70	$76.70
Purchase #3	$169.43	11.846%	$189.5007	$189.50	$189.50	$189.50
Purchase #4	$93.84	7.412%	$100.7954	$100.80	$100.80	$100.80
Purchase #5	$24.53	11.182%	$27.2729	$27.27	$27.25	$27.30
Purchase #6	$157.82	3.266%	$162.9744	$162.97	$162.95	$163.00
Purchase #7	$126.57	10.503%	$139.8636	$139.86	$139.85	$139.90
7 purchase totals =	$724.72		$786.6863	$786.68	$786.60	$786.80