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	$234.76	5.133%	$246.8102	$246.81	$246.80	$246.80
Purchase #2	$146.25	10.583%	$161.7276	$161.73	$161.75	$161.70
Purchase #3	$174.48	6.365%	$185.5857	$185.59	$185.60	$185.60
Purchase #4	$78.64	13.625%	$89.3547	$89.35	$89.35	$89.40
Purchase #5	$52.67	11.653%	$58.8076	$58.81	$58.80	$58.80
Purchase #6	$158.71	6.431%	$168.9166	$168.92	$168.90	$168.90
Purchase #7	$158.68	6.669%	$169.2624	$169.26	$169.25	$169.30
7 purchase totals =	$1,004.19		$1,080.4648	$1,080.47	$1,080.45	$1,080.50