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	$43.85	4.590%	$45.8627	$45.86	$45.85	$45.90
Purchase #2	$58.26	12.496%	$65.5402	$65.54	$65.55	$65.50
Purchase #3	$174.93	10.820%	$193.8574	$193.86	$193.85	$193.90
Purchase #4	$230.34	10.862%	$255.3595	$255.36	$255.35	$255.40
Purchase #5	$9.56	5.394%	$10.0757	$10.08	$10.10	$10.10
Purchase #6	$37.53	12.859%	$42.356	$42.36	$42.35	$42.40
Purchase #7	$25.37	7.704%	$27.3245	$27.32	$27.30	$27.30
7 purchase totals =	$579.84		$640.3760	$640.38	$640.35	$640.50