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	$56.82	13.178%	$64.3077	$64.31	$64.30	$64.30
Purchase #2	$62.56	8.350%	$67.7838	$67.78	$67.80	$67.80
Purchase #3	$219.59	5.423%	$231.4984	$231.50	$231.50	$231.50
Purchase #4	$175.33	8.360%	$189.9876	$189.99	$190.00	$190.00
Purchase #5	$15.57	9.741%	$17.0867	$17.09	$17.10	$17.10
Purchase #6	$94.61	9.285%	$103.3945	$103.39	$103.40	$103.40
Purchase #7	$123.58	10.476%	$136.5262	$136.53	$136.55	$136.50
7 purchase totals =	$748.06		$810.5849	$810.59	$810.65	$810.60