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	$123.86	11.298%	$137.8537	$137.85	$137.85	$137.90
Purchase #2	$129.62	10.143%	$142.7674	$142.77	$142.75	$142.80
Purchase #3	$39.61	5.163%	$41.6551	$41.66	$41.65	$41.70
Purchase #4	$77.57	6.366%	$82.5081	$82.51	$82.50	$82.50
Purchase #5	$218.59	10.200%	$240.8862	$240.89	$240.90	$240.90
Purchase #6	$29.61	11.286%	$32.9518	$32.95	$32.95	$33.00
Purchase #7	$92.98	3.197%	$95.9526	$95.95	$95.95	$96.00
7 purchase totals =	$711.84		$774.5749	$774.58	$774.55	$774.80