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	$81.43	11.600%	$90.8759	$90.88	$90.90	$90.90
Purchase #2	$188.26	4.636%	$196.9877	$196.99	$197.00	$197.00
Purchase #3	$109.50	3.104%	$112.8989	$112.90	$112.90	$112.90
Purchase #4	$137.99	12.164%	$154.7751	$154.78	$154.80	$154.80
Purchase #5	$99.29	9.695%	$108.9162	$108.92	$108.90	$108.90
Purchase #6	$83.86	7.606%	$90.2384	$90.24	$90.25	$90.20
Purchase #7	$214.31	6.515%	$228.2723	$228.27	$228.25	$228.30
7 purchase totals =	$914.64		$982.9645	$982.98	$983.00	$983.00