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	$70.28	11.440%	$78.32	$78.32	$78.30	$78.30
Purchase #2	$190.60	13.241%	$215.8373	$215.84	$215.85	$215.80
Purchase #3	$76.93	8.520%	$83.4844	$83.48	$83.50	$83.50
Purchase #4	$57.35	7.829%	$61.8399	$61.84	$61.85	$61.80
Purchase #5	$49.36	9.246%	$53.9238	$53.92	$53.90	$53.90
Purchase #6	$135.28	5.256%	$142.3903	$142.39	$142.40	$142.40
Purchase #7	$120.67	9.233%	$131.8115	$131.81	$131.80	$131.80
7 purchase totals =	$700.47		$767.6072	$767.60	$767.60	$767.50