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	$74.44	10.552%	$82.2949	$82.29	$82.30	$82.30
Purchase #2	$144.71	6.860%	$154.6371	$154.64	$154.65	$154.60
Purchase #3	$237.79	13.233%	$269.2568	$269.26	$269.25	$269.30
Purchase #4	$78.45	9.377%	$85.8063	$85.81	$85.80	$85.80
Purchase #5	$63.81	4.852%	$66.9061	$66.91	$66.90	$66.90
Purchase #6	$86.77	6.438%	$92.3563	$92.36	$92.35	$92.40
Purchase #7	$61.82	12.156%	$69.3348	$69.33	$69.35	$69.30
7 purchase totals =	$747.79		$820.5923	$820.60	$820.60	$820.60