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	$62.28	7.735%	$67.0974	$67.10	$67.10	$67.10
Purchase #2	$128.40	4.815%	$134.5825	$134.58	$134.60	$134.60
Purchase #3	$50.49	9.196%	$55.1331	$55.13	$55.15	$55.10
Purchase #4	$134.49	3.520%	$139.224	$139.22	$139.20	$139.20
Purchase #5	$85.98	5.445%	$90.6616	$90.66	$90.65	$90.70
Purchase #6	$53.64	3.367%	$55.4461	$55.45	$55.45	$55.40
Purchase #7	$35.33	5.293%	$37.2	$37.20	$37.20	$37.20
7 purchase totals =	$550.61		$579.3447	$579.34	$579.35	$579.30