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	$37.45	12.826%	$42.2533	$42.25	$42.25	$42.30
Purchase #2	$179.46	9.119%	$195.825	$195.83	$195.85	$195.80
Purchase #3	$39.58	6.468%	$42.14	$42.14	$42.15	$42.10
Purchase #4	$103.29	10.323%	$113.9526	$113.95	$113.95	$114.00
Purchase #5	$156.54	7.167%	$167.7592	$167.76	$167.75	$167.80
Purchase #6	$182.61	3.685%	$189.3392	$189.34	$189.35	$189.30
Purchase #7	$22.90	3.282%	$23.6516	$23.65	$23.65	$23.70
7 purchase totals =	$721.83		$774.9209	$774.92	$774.95	$775.00