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	$48.37	6.458%	$51.4937	$51.49	$51.50	$51.50
Purchase #2	$142.48	10.720%	$157.7539	$157.75	$157.75	$157.80
Purchase #3	$75.91	12.383%	$85.3099	$85.31	$85.30	$85.30
Purchase #4	$165.58	8.866%	$180.2603	$180.26	$180.25	$180.30
Purchase #5	$39.89	3.201%	$41.1669	$41.17	$41.15	$41.20
Purchase #6	$82.54	3.392%	$85.3398	$85.34	$85.35	$85.30
Purchase #7	$39.92	5.466%	$42.102	$42.10	$42.10	$42.10
7 purchase totals =	$594.69		$643.4265	$643.42	$643.40	$643.50