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	$33.94	11.672%	$37.9015	$37.90	$37.90	$37.90
Purchase #2	$188.67	5.721%	$199.4638	$199.46	$199.45	$199.50
Purchase #3	$24.43	4.192%	$25.4541	$25.45	$25.45	$25.50
Purchase #4	$24.58	10.820%	$27.2396	$27.24	$27.25	$27.20
Purchase #5	$56.69	12.684%	$63.8806	$63.88	$63.90	$63.90
Purchase #6	$24.25	7.472%	$26.062	$26.06	$26.05	$26.10
Purchase #7	$145.88	8.514%	$158.3002	$158.30	$158.30	$158.30
7 purchase totals =	$498.44		$538.3018	$538.29	$538.30	$538.40