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	$137.36	8.396%	$148.8927	$148.89	$148.90	$148.90
Purchase #2	$45.78	4.719%	$47.9404	$47.94	$47.95	$47.90
Purchase #3	$43.29	5.184%	$45.5342	$45.53	$45.55	$45.50
Purchase #4	$225.65	9.605%	$247.3237	$247.32	$247.30	$247.30
Purchase #5	$82.75	12.111%	$92.7719	$92.77	$92.75	$92.80
Purchase #6	$46.90	9.613%	$51.4085	$51.41	$51.40	$51.40
Purchase #7	$80.76	8.274%	$87.4421	$87.44	$87.45	$87.40
7 purchase totals =	$662.49		$721.3135	$721.30	$721.30	$721.20