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	$24.73	4.806%	$25.9185	$25.92	$25.90	$25.90
Purchase #2	$212.50	11.477%	$236.8886	$236.89	$236.90	$236.90
Purchase #3	$107.30	12.222%	$120.4142	$120.41	$120.40	$120.40
Purchase #4	$222.64	8.351%	$241.2327	$241.23	$241.25	$241.20
Purchase #5	$16.60	12.116%	$18.6113	$18.61	$18.60	$18.60
Purchase #6	$175.41	6.613%	$187.0099	$187.01	$187.00	$187.00
Purchase #7	$173.73	9.680%	$190.5471	$190.55	$190.55	$190.50
7 purchase totals =	$932.91		$1,020.6223	$1,020.62	$1,020.60	$1,020.50