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	$77.75	10.229%	$85.703	$85.70	$85.70	$85.70
Purchase #2	$150.58	12.543%	$169.4672	$169.47	$169.45	$169.50
Purchase #3	$81.50	10.415%	$89.9882	$89.99	$90.00	$90.00
Purchase #4	$109.79	10.671%	$121.5057	$121.51	$121.50	$121.50
Purchase #5	$12.33	11.775%	$13.7819	$13.78	$13.80	$13.80
Purchase #6	$224.38	13.853%	$255.4634	$255.46	$255.45	$255.50
Purchase #7	$165.55	5.714%	$175.0095	$175.01	$175.00	$175.00
7 purchase totals =	$821.88		$910.9189	$910.92	$910.90	$911.00