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	$180.45	11.120%	$200.516	$200.52	$200.50	$200.50
Purchase #2	$83.86	9.523%	$91.846	$91.85	$91.85	$91.80
Purchase #3	$39.68	4.489%	$41.4612	$41.46	$41.45	$41.50
Purchase #4	$94.77	13.148%	$107.2304	$107.23	$107.25	$107.20
Purchase #5	$46.50	13.363%	$52.7138	$52.71	$52.70	$52.70
Purchase #6	$27.60	3.569%	$28.585	$28.59	$28.60	$28.60
Purchase #7	$69.83	13.406%	$79.1914	$79.19	$79.20	$79.20
7 purchase totals =	$542.69		$601.5438	$601.55	$601.55	$601.50