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	$97.91	5.307%	$103.1061	$103.11	$103.10	$103.10
Purchase #2	$99.90	8.622%	$108.5134	$108.51	$108.50	$108.50
Purchase #3	$151.60	3.804%	$157.3669	$157.37	$157.35	$157.40
Purchase #4	$56.63	4.564%	$59.2146	$59.21	$59.20	$59.20
Purchase #5	$37.61	7.784%	$40.5376	$40.54	$40.55	$40.50
Purchase #6	$195.59	12.367%	$219.7786	$219.78	$219.80	$219.80
Purchase #7	$111.52	7.167%	$119.5126	$119.51	$119.50	$119.50
7 purchase totals =	$750.76		$808.0298	$808.03	$808.00	$808.00