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	$249.96	13.628%	$284.0245	$284.02	$284.00	$284.00
Purchase #2	$45.27	5.482%	$47.7517	$47.75	$47.75	$47.80
Purchase #3	$215.56	4.377%	$224.9951	$225.00	$225.00	$225.00
Purchase #4	$139.71	13.753%	$158.9243	$158.92	$158.90	$158.90
Purchase #5	$112.41	6.527%	$119.747	$119.75	$119.75	$119.70
Purchase #6	$128.56	12.714%	$144.9051	$144.91	$144.90	$144.90
Purchase #7	$220.32	10.245%	$242.8918	$242.89	$242.90	$242.90
7 purchase totals =	$1,111.79		$1,223.2395	$1,223.24	$1,223.20	$1,223.20