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	$62.40	6.392%	$66.3886	$66.39	$66.40	$66.40
Purchase #2	$66.45	9.134%	$72.5195	$72.52	$72.50	$72.50
Purchase #3	$175.99	11.460%	$196.1585	$196.16	$196.15	$196.20
Purchase #4	$101.89	13.860%	$116.012	$116.01	$116.00	$116.00
Purchase #5	$191.48	9.619%	$209.8985	$209.90	$209.90	$209.90
Purchase #6	$13.56	5.549%	$14.3124	$14.31	$14.30	$14.30
Purchase #7	$139.56	9.840%	$153.2927	$153.29	$153.30	$153.30
7 purchase totals =	$751.33		$828.5822	$828.58	$828.55	$828.60