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	$14.68	8.565%	$15.9373	$15.94	$15.95	$15.90
Purchase #2	$220.41	10.419%	$243.3745	$243.37	$243.35	$243.40
Purchase #3	$204.31	6.463%	$217.5146	$217.51	$217.50	$217.50
Purchase #4	$54.33	9.705%	$59.6027	$59.60	$59.60	$59.60
Purchase #5	$27.91	10.842%	$30.936	$30.94	$30.95	$30.90
Purchase #6	$89.89	6.313%	$95.5648	$95.56	$95.55	$95.60
Purchase #7	$16.85	9.205%	$18.401	$18.40	$18.40	$18.40
7 purchase totals =	$628.38		$681.3309	$681.32	$681.30	$681.30