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	$107.25	7.369%	$115.1533	$115.15	$115.15	$115.20
Purchase #2	$127.94	12.761%	$144.2664	$144.27	$144.25	$144.30
Purchase #3	$44.28	10.115%	$48.7589	$48.76	$48.75	$48.80
Purchase #4	$212.64	3.715%	$220.5396	$220.54	$220.55	$220.50
Purchase #5	$79.69	3.632%	$82.5843	$82.58	$82.60	$82.60
Purchase #6	$193.90	3.599%	$200.8785	$200.88	$200.90	$200.90
Purchase #7	$56.73	4.826%	$59.4678	$59.47	$59.45	$59.50
7 purchase totals =	$822.43		$871.6488	$871.65	$871.65	$871.80