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	$134.48	7.224%	$144.1948	$144.19	$144.20	$144.20
Purchase #2	$90.36	11.231%	$100.5083	$100.51	$100.50	$100.50
Purchase #3	$46.44	5.127%	$48.821	$48.82	$48.80	$48.80
Purchase #4	$45.78	12.104%	$51.3212	$51.32	$51.30	$51.30
Purchase #5	$39.48	5.316%	$41.5788	$41.58	$41.60	$41.60
Purchase #6	$139.51	4.523%	$145.82	$145.82	$145.80	$145.80
Purchase #7	$192.56	9.732%	$211.2999	$211.30	$211.30	$211.30
7 purchase totals =	$688.61		$743.5440	$743.54	$743.50	$743.50