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	$175.31	5.824%	$185.5201	$185.52	$185.50	$185.50
Purchase #2	$29.89	4.109%	$31.1182	$31.12	$31.10	$31.10
Purchase #3	$213.96	9.735%	$234.789	$234.79	$234.80	$234.80
Purchase #4	$88.87	13.668%	$101.0168	$101.02	$101.00	$101.00
Purchase #5	$195.84	13.702%	$222.674	$222.67	$222.65	$222.70
Purchase #6	$28.94	8.384%	$31.3663	$31.37	$31.35	$31.40
Purchase #7	$118.96	10.623%	$131.5971	$131.60	$131.60	$131.60
7 purchase totals =	$851.77		$938.0815	$938.09	$938.00	$938.10