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	$117.91	5.591%	$124.5023	$124.50	$124.50	$124.50
Purchase #2	$57.51	12.342%	$64.6079	$64.61	$64.60	$64.60
Purchase #3	$79.31	9.527%	$86.8659	$86.87	$86.85	$86.90
Purchase #4	$47.72	12.353%	$53.6149	$53.61	$53.60	$53.60
Purchase #5	$36.47	7.162%	$39.082	$39.08	$39.10	$39.10
Purchase #6	$78.78	4.379%	$82.2298	$82.23	$82.25	$82.20
Purchase #7	$144.77	9.515%	$158.5449	$158.54	$158.55	$158.50
7 purchase totals =	$562.47		$609.4477	$609.44	$609.45	$609.40