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	$80.58	11.473%	$89.8249	$89.82	$89.80	$89.80
Purchase #2	$105.44	11.149%	$117.1955	$117.20	$117.20	$117.20
Purchase #3	$177.72	6.124%	$188.6036	$188.60	$188.60	$188.60
Purchase #4	$16.72	13.356%	$18.9531	$18.95	$18.95	$19.00
Purchase #5	$249.86	11.775%	$279.281	$279.28	$279.30	$279.30
Purchase #6	$169.89	10.376%	$187.5178	$187.52	$187.50	$187.50
Purchase #7	$198.57	11.645%	$221.6935	$221.69	$221.70	$221.70
7 purchase totals =	$998.78		$1,103.0694	$1,103.06	$1,103.05	$1,103.10