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	$48.71	13.478%	$55.2751	$55.28	$55.30	$55.30
Purchase #2	$174.50	9.237%	$190.6186	$190.62	$190.60	$190.60
Purchase #3	$79.96	6.737%	$85.3469	$85.35	$85.35	$85.30
Purchase #4	$53.99	11.196%	$60.0347	$60.03	$60.05	$60.00
Purchase #5	$37.56	8.367%	$40.7026	$40.70	$40.70	$40.70
Purchase #6	$60.46	11.654%	$67.506	$67.51	$67.50	$67.50
Purchase #7	$63.41	4.834%	$66.4752	$66.48	$66.50	$66.50
7 purchase totals =	$518.59		$565.9591	$565.97	$566.00	$565.90