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	$84.28	5.674%	$89.062	$89.06	$89.05	$89.10
Purchase #2	$130.98	7.121%	$140.3071	$140.31	$140.30	$140.30
Purchase #3	$140.33	5.764%	$148.4186	$148.42	$148.40	$148.40
Purchase #4	$248.85	3.206%	$256.8281	$256.83	$256.85	$256.80
Purchase #5	$173.61	10.636%	$192.0752	$192.08	$192.10	$192.10
Purchase #6	$88.40	13.766%	$100.5691	$100.57	$100.55	$100.60
Purchase #7	$141.36	4.423%	$147.6124	$147.61	$147.60	$147.60
7 purchase totals =	$1,007.81		$1,074.8725	$1,074.88	$1,074.85	$1,074.90