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	$47.58	6.134%	$50.4986	$50.50	$50.50	$50.50
Purchase #2	$102.90	12.388%	$115.6473	$115.65	$115.65	$115.60
Purchase #3	$139.52	8.547%	$151.4448	$151.44	$151.45	$151.40
Purchase #4	$141.62	13.234%	$160.362	$160.36	$160.35	$160.40
Purchase #5	$64.41	10.760%	$71.3405	$71.34	$71.35	$71.30
Purchase #6	$51.86	5.783%	$54.8591	$54.86	$54.85	$54.90
Purchase #7	$7.45	6.337%	$7.9221	$7.92	$7.90	$7.90
7 purchase totals =	$555.34		$612.0744	$612.07	$612.05	$612.00