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	$68.79	9.219%	$75.1318	$75.13	$75.15	$75.10
Purchase #2	$95.78	10.716%	$106.0438	$106.04	$106.05	$106.00
Purchase #3	$16.85	10.783%	$18.6669	$18.67	$18.65	$18.70
Purchase #4	$178.51	9.156%	$194.8544	$194.85	$194.85	$194.90
Purchase #5	$78.93	13.759%	$89.79	$89.79	$89.80	$89.80
Purchase #6	$59.35	5.345%	$62.5223	$62.52	$62.50	$62.50
Purchase #7	$108.63	11.232%	$120.8313	$120.83	$120.85	$120.80
7 purchase totals =	$606.84		$667.8405	$667.83	$667.85	$667.80