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	$137.40	6.429%	$146.2334	$146.23	$146.25	$146.20
Purchase #2	$205.55	7.848%	$221.6816	$221.68	$221.70	$221.70
Purchase #3	$89.64	7.359%	$96.2366	$96.24	$96.25	$96.20
Purchase #4	$241.36	5.246%	$254.0217	$254.02	$254.00	$254.00
Purchase #5	$172.83	9.291%	$188.8876	$188.89	$188.90	$188.90
Purchase #6	$25.82	12.202%	$28.9706	$28.97	$28.95	$29.00
Purchase #7	$74.91	7.655%	$80.6444	$80.64	$80.65	$80.60
7 purchase totals =	$947.51		$1,016.6759	$1,016.67	$1,016.70	$1,016.60