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	$18.90	6.127%	$20.058	$20.06	$20.05	$20.10
Purchase #2	$63.63	4.152%	$66.2719	$66.27	$66.25	$66.30
Purchase #3	$199.83	7.668%	$215.153	$215.15	$215.15	$215.20
Purchase #4	$161.40	11.676%	$180.2451	$180.25	$180.25	$180.20
Purchase #5	$104.58	6.357%	$111.2282	$111.23	$111.25	$111.20
Purchase #6	$226.30	10.261%	$249.5206	$249.52	$249.50	$249.50
Purchase #7	$136.91	12.526%	$154.0593	$154.06	$154.05	$154.10
7 purchase totals =	$911.55		$996.5361	$996.54	$996.50	$996.60