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	$29.68	6.343%	$31.5626	$31.56	$31.55	$31.60
Purchase #2	$111.76	7.484%	$120.1241	$120.12	$120.10	$120.10
Purchase #3	$248.93	11.110%	$276.5861	$276.59	$276.60	$276.60
Purchase #4	$19.86	9.864%	$21.819	$21.82	$21.80	$21.80
Purchase #5	$229.27	9.423%	$250.8741	$250.87	$250.85	$250.90
Purchase #6	$200.50	9.706%	$219.9605	$219.96	$219.95	$220.00
Purchase #7	$158.49	5.314%	$166.9122	$166.91	$166.90	$166.90
7 purchase totals =	$998.49		$1,087.8386	$1,087.83	$1,087.75	$1,087.90