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	$66.65	9.321%	$72.8624	$72.86	$72.85	$72.90
Purchase #2	$203.43	7.224%	$218.1258	$218.13	$218.15	$218.10
Purchase #3	$135.31	13.706%	$153.8556	$153.86	$153.85	$153.90
Purchase #4	$128.89	10.484%	$142.4028	$142.40	$142.40	$142.40
Purchase #5	$142.51	5.657%	$150.5718	$150.57	$150.55	$150.60
Purchase #6	$128.47	3.211%	$132.5952	$132.60	$132.60	$132.60
Purchase #7	$94.86	5.805%	$100.3666	$100.37	$100.35	$100.40
7 purchase totals =	$900.12		$970.7802	$970.79	$970.75	$970.90