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	$139.37	7.822%	$150.2715	$150.27	$150.25	$150.30
Purchase #2	$131.31	8.144%	$142.0039	$142.00	$142.00	$142.00
Purchase #3	$74.46	4.592%	$77.8792	$77.88	$77.90	$77.90
Purchase #4	$21.27	6.163%	$22.5809	$22.58	$22.60	$22.60
Purchase #5	$179.41	11.513%	$200.0655	$200.07	$200.05	$200.10
Purchase #6	$35.85	12.391%	$40.2922	$40.29	$40.30	$40.30
Purchase #7	$141.68	8.410%	$153.5953	$153.60	$153.60	$153.60
7 purchase totals =	$723.35		$786.6885	$786.69	$786.70	$786.80