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	$19.82	7.135%	$21.2342	$21.23	$21.25	$21.20
Purchase #2	$154.96	11.385%	$172.6022	$172.60	$172.60	$172.60
Purchase #3	$11.30	3.283%	$11.671	$11.67	$11.65	$11.70
Purchase #4	$59.97	12.227%	$67.3025	$67.30	$67.30	$67.30
Purchase #5	$151.50	12.454%	$170.3678	$170.37	$170.35	$170.40
Purchase #6	$96.55	4.562%	$100.9546	$100.95	$100.95	$101.00
Purchase #7	$111.59	7.398%	$119.8454	$119.85	$119.85	$119.80
7 purchase totals =	$605.69		$663.9777	$663.97	$663.95	$664.00