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	$22.78	9.353%	$24.9106	$24.91	$24.90	$24.90
Purchase #2	$135.55	9.521%	$148.4557	$148.46	$148.45	$148.50
Purchase #3	$10.41	13.314%	$11.796	$11.80	$11.80	$11.80
Purchase #4	$149.82	10.765%	$165.9481	$165.95	$165.95	$165.90
Purchase #5	$62.84	4.196%	$65.4768	$65.48	$65.50	$65.50
Purchase #6	$228.40	11.159%	$253.8872	$253.89	$253.90	$253.90
Purchase #7	$142.61	4.548%	$149.0959	$149.10	$149.10	$149.10
7 purchase totals =	$752.41		$819.5703	$819.59	$819.60	$819.60