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	$81.40	9.424%	$89.0711	$89.07	$89.05	$89.10
Purchase #2	$198.48	11.465%	$221.2357	$221.24	$221.25	$221.20
Purchase #3	$28.38	13.245%	$32.1389	$32.14	$32.15	$32.10
Purchase #4	$95.35	10.704%	$105.5563	$105.56	$105.55	$105.60
Purchase #5	$131.89	12.480%	$148.3499	$148.35	$148.35	$148.30
Purchase #6	$91.64	9.288%	$100.1515	$100.15	$100.15	$100.20
Purchase #7	$234.76	13.345%	$266.0887	$266.09	$266.10	$266.10
7 purchase totals =	$861.90		$962.5921	$962.60	$962.60	$962.60