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	$86.70	5.357%	$91.3445	$91.34	$91.35	$91.30
Purchase #2	$41.37	12.603%	$46.5839	$46.58	$46.60	$46.60
Purchase #3	$204.33	12.341%	$229.5464	$229.55	$229.55	$229.50
Purchase #4	$29.57	13.303%	$33.5037	$33.50	$33.50	$33.50
Purchase #5	$46.45	9.572%	$50.8962	$50.90	$50.90	$50.90
Purchase #6	$169.72	3.590%	$175.8129	$175.81	$175.80	$175.80
Purchase #7	$194.71	5.233%	$204.8992	$204.90	$204.90	$204.90
7 purchase totals =	$772.85		$832.5868	$832.58	$832.60	$832.50