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	$137.30	10.627%	$151.8909	$151.89	$151.90	$151.90
Purchase #2	$54.61	8.521%	$59.2633	$59.26	$59.25	$59.30
Purchase #3	$172.94	12.641%	$194.8013	$194.80	$194.80	$194.80
Purchase #4	$185.38	5.706%	$195.9578	$195.96	$195.95	$196.00
Purchase #5	$182.98	6.862%	$195.5361	$195.54	$195.55	$195.50
Purchase #6	$41.96	13.805%	$47.7526	$47.75	$47.75	$47.80
Purchase #7	$145.70	3.377%	$150.6203	$150.62	$150.60	$150.60
7 purchase totals =	$920.87		$995.8223	$995.82	$995.80	$995.90