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	$238.71	13.359%	$270.5993	$270.60	$270.60	$270.60
Purchase #2	$184.82	13.525%	$209.8169	$209.82	$209.80	$209.80
Purchase #3	$238.38	11.254%	$265.2073	$265.21	$265.20	$265.20
Purchase #4	$155.61	6.241%	$165.3216	$165.32	$165.30	$165.30
Purchase #5	$51.79	8.324%	$56.101	$56.10	$56.10	$56.10
Purchase #6	$24.76	3.180%	$25.5474	$25.55	$25.55	$25.50
Purchase #7	$198.89	12.631%	$224.0118	$224.01	$224.00	$224.00
7 purchase totals =	$1,092.96		$1,216.6053	$1,216.61	$1,216.55	$1,216.50