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	$52.45	8.829%	$57.0808	$57.08	$57.10	$57.10
Purchase #2	$48.90	8.490%	$53.0516	$53.05	$53.05	$53.10
Purchase #3	$188.40	6.489%	$200.6253	$200.63	$200.65	$200.60
Purchase #4	$85.85	6.449%	$91.3865	$91.39	$91.40	$91.40
Purchase #5	$79.71	7.366%	$85.5814	$85.58	$85.60	$85.60
Purchase #6	$32.33	6.638%	$34.4761	$34.48	$34.50	$34.50
Purchase #7	$134.40	4.300%	$140.1792	$140.18	$140.20	$140.20
7 purchase totals =	$622.04		$662.3809	$662.39	$662.50	$662.50