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	$95.74	3.688%	$99.2709	$99.27	$99.25	$99.30
Purchase #2	$46.82	12.413%	$52.6318	$52.63	$52.65	$52.60
Purchase #3	$128.74	4.560%	$134.6105	$134.61	$134.60	$134.60
Purchase #4	$159.65	13.108%	$180.5769	$180.58	$180.60	$180.60
Purchase #5	$166.47	8.434%	$180.5101	$180.51	$180.50	$180.50
Purchase #6	$77.37	7.557%	$83.2169	$83.22	$83.20	$83.20
Purchase #7	$244.89	10.498%	$270.5986	$270.60	$270.60	$270.60
7 purchase totals =	$919.68		$1,001.4157	$1,001.42	$1,001.40	$1,001.40