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	$182.40	12.516%	$205.2292	$205.23	$205.25	$205.20
Purchase #2	$160.86	10.762%	$178.1718	$178.17	$178.15	$178.20
Purchase #3	$139.90	10.524%	$154.6231	$154.62	$154.60	$154.60
Purchase #4	$131.83	7.483%	$141.6948	$141.69	$141.70	$141.70
Purchase #5	$85.56	4.308%	$89.2459	$89.25	$89.25	$89.20
Purchase #6	$213.92	11.440%	$238.3924	$238.39	$238.40	$238.40
Purchase #7	$233.28	7.629%	$251.0769	$251.08	$251.10	$251.10
7 purchase totals =	$1,147.75		$1,258.4341	$1,258.43	$1,258.45	$1,258.40