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	$36.27	4.479%	$37.8945	$37.89	$37.90	$37.90
Purchase #2	$234.74	6.651%	$250.3526	$250.35	$250.35	$250.40
Purchase #3	$71.47	10.356%	$78.8714	$78.87	$78.85	$78.90
Purchase #4	$166.61	4.299%	$173.7726	$173.77	$173.75	$173.80
Purchase #5	$142.72	12.670%	$160.8026	$160.80	$160.80	$160.80
Purchase #6	$183.83	8.300%	$199.0879	$199.09	$199.10	$199.10
Purchase #7	$52.35	7.833%	$56.4506	$56.45	$56.45	$56.50
7 purchase totals =	$887.99		$957.2322	$957.22	$957.20	$957.40