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	$186.61	5.519%	$196.909	$196.91	$196.90	$196.90
Purchase #2	$53.78	13.641%	$61.1161	$61.12	$61.10	$61.10
Purchase #3	$34.69	8.679%	$37.7007	$37.70	$37.70	$37.70
Purchase #4	$131.34	6.247%	$139.5448	$139.54	$139.55	$139.50
Purchase #5	$235.55	5.620%	$248.7879	$248.79	$248.80	$248.80
Purchase #6	$120.48	13.758%	$137.0556	$137.06	$137.05	$137.10
Purchase #7	$148.43	13.435%	$168.3716	$168.37	$168.35	$168.40
7 purchase totals =	$910.88		$989.4857	$989.49	$989.45	$989.50