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	$111.62	10.203%	$123.0086	$123.01	$123.00	$123.00
Purchase #2	$44.59	13.323%	$50.5307	$50.53	$50.55	$50.50
Purchase #3	$81.84	9.795%	$89.8562	$89.86	$89.85	$89.90
Purchase #4	$188.45	5.383%	$198.5943	$198.59	$198.60	$198.60
Purchase #5	$25.96	10.296%	$28.6328	$28.63	$28.65	$28.60
Purchase #6	$143.76	12.668%	$161.9715	$161.97	$161.95	$162.00
Purchase #7	$177.28	6.354%	$188.5444	$188.54	$188.55	$188.50
7 purchase totals =	$773.50		$841.1385	$841.13	$841.15	$841.10