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	$36.67	5.470%	$38.6758	$38.68	$38.70	$38.70
Purchase #2	$99.86	4.727%	$104.5804	$104.58	$104.60	$104.60
Purchase #3	$36.98	8.598%	$40.1595	$40.16	$40.15	$40.20
Purchase #4	$59.80	13.471%	$67.8557	$67.86	$67.85	$67.90
Purchase #5	$100.46	12.714%	$113.2325	$113.23	$113.25	$113.20
Purchase #6	$154.88	7.166%	$165.9787	$165.98	$166.00	$166.00
Purchase #7	$106.36	3.858%	$110.4634	$110.46	$110.45	$110.50
7 purchase totals =	$595.01		$640.9460	$640.95	$641.00	$641.10