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	$29.79	7.506%	$32.026	$32.03	$32.05	$32.00
Purchase #2	$59.55	9.828%	$65.4026	$65.40	$65.40	$65.40
Purchase #3	$62.82	10.346%	$69.3194	$69.32	$69.30	$69.30
Purchase #4	$115.97	13.168%	$131.2409	$131.24	$131.25	$131.20
Purchase #5	$233.32	9.301%	$255.0211	$255.02	$255.00	$255.00
Purchase #6	$88.96	10.818%	$98.5837	$98.58	$98.60	$98.60
Purchase #7	$37.65	4.263%	$39.255	$39.26	$39.25	$39.30
7 purchase totals =	$628.06		$690.8487	$690.85	$690.85	$690.80