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	$92.89	10.767%	$102.8915	$102.89	$102.90	$102.90
Purchase #2	$213.80	9.626%	$234.3804	$234.38	$234.40	$234.40
Purchase #3	$152.52	8.630%	$165.6825	$165.68	$165.70	$165.70
Purchase #4	$13.48	13.489%	$15.2983	$15.30	$15.30	$15.30
Purchase #5	$100.76	3.567%	$104.3541	$104.35	$104.35	$104.40
Purchase #6	$45.59	6.155%	$48.3961	$48.40	$48.40	$48.40
Purchase #7	$174.87	6.293%	$185.8746	$185.87	$185.85	$185.90
7 purchase totals =	$793.91		$856.8775	$856.87	$856.90	$857.00