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	$11.33	10.290%	$12.4959	$12.50	$12.50	$12.50
Purchase #2	$230.85	4.463%	$241.1528	$241.15	$241.15	$241.20
Purchase #3	$53.66	10.653%	$59.3764	$59.38	$59.40	$59.40
Purchase #4	$157.61	8.673%	$171.2795	$171.28	$171.30	$171.30
Purchase #5	$112.86	10.221%	$124.3954	$124.40	$124.40	$124.40
Purchase #6	$86.58	12.853%	$97.7081	$97.71	$97.70	$97.70
Purchase #7	$237.26	11.463%	$264.4571	$264.46	$264.45	$264.50
7 purchase totals =	$890.15		$970.8652	$970.88	$970.90	$971.00