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	$36.54	8.158%	$39.5209	$39.52	$39.50	$39.50
Purchase #2	$74.62	6.269%	$79.2979	$79.30	$79.30	$79.30
Purchase #3	$167.57	10.465%	$185.1062	$185.11	$185.10	$185.10
Purchase #4	$88.78	11.480%	$98.9719	$98.97	$98.95	$99.00
Purchase #5	$133.83	8.236%	$144.8522	$144.85	$144.85	$144.90
Purchase #6	$79.84	13.375%	$90.5186	$90.52	$90.50	$90.50
Purchase #7	$237.82	9.268%	$259.8612	$259.86	$259.85	$259.90
7 purchase totals =	$819.00		$898.1289	$898.13	$898.05	$898.20