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	$11.94	10.291%	$13.1687	$13.17	$13.15	$13.20
Purchase #2	$94.56	4.696%	$99.0005	$99.00	$99.00	$99.00
Purchase #3	$164.39	12.766%	$185.376	$185.38	$185.40	$185.40
Purchase #4	$153.81	12.473%	$172.9947	$172.99	$173.00	$173.00
Purchase #5	$95.92	9.535%	$105.066	$105.07	$105.05	$105.10
Purchase #6	$98.76	10.697%	$109.3244	$109.32	$109.30	$109.30
Purchase #7	$194.98	12.765%	$219.8692	$219.87	$219.85	$219.90
7 purchase totals =	$814.36		$904.7995	$904.80	$904.75	$904.90