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	$36.50	5.536%	$38.5206	$38.52	$38.50	$38.50
Purchase #2	$167.81	9.133%	$183.1361	$183.14	$183.15	$183.10
Purchase #3	$39.86	4.768%	$41.7605	$41.76	$41.75	$41.80
Purchase #4	$240.51	9.684%	$263.801	$263.80	$263.80	$263.80
Purchase #5	$169.89	12.748%	$191.5476	$191.55	$191.55	$191.50
Purchase #6	$159.25	4.185%	$165.9146	$165.91	$165.90	$165.90
Purchase #7	$20.53	5.222%	$21.6021	$21.60	$21.60	$21.60
7 purchase totals =	$834.35		$906.2825	$906.28	$906.25	$906.20