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	$57.85	3.598%	$59.9314	$59.93	$59.95	$59.90
Purchase #2	$36.51	7.648%	$39.3023	$39.30	$39.30	$39.30
Purchase #3	$63.44	8.351%	$68.7379	$68.74	$68.75	$68.70
Purchase #4	$78.28	5.358%	$82.4742	$82.47	$82.45	$82.50
Purchase #5	$89.51	6.331%	$95.1769	$95.18	$95.20	$95.20
Purchase #6	$223.71	6.615%	$238.5084	$238.51	$238.50	$238.50
Purchase #7	$230.81	10.393%	$254.7981	$254.80	$254.80	$254.80
7 purchase totals =	$780.11		$838.9292	$838.93	$838.95	$838.90