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	$150.33	10.109%	$165.5269	$165.53	$165.55	$165.50
Purchase #2	$203.86	8.291%	$220.762	$220.76	$220.75	$220.80
Purchase #3	$77.35	10.667%	$85.6009	$85.60	$85.60	$85.60
Purchase #4	$169.38	6.527%	$180.4354	$180.44	$180.45	$180.40
Purchase #5	$31.88	7.451%	$34.2554	$34.26	$34.25	$34.30
Purchase #6	$103.40	13.781%	$117.6496	$117.65	$117.65	$117.60
Purchase #7	$97.37	12.851%	$109.883	$109.88	$109.90	$109.90
7 purchase totals =	$833.57		$914.1132	$914.12	$914.15	$914.10