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	$235.43	12.183%	$264.1124	$264.11	$264.10	$264.10
Purchase #2	$141.58	10.635%	$156.637	$156.64	$156.65	$156.60
Purchase #3	$62.31	13.205%	$70.538	$70.54	$70.55	$70.50
Purchase #4	$107.48	8.291%	$116.3912	$116.39	$116.40	$116.40
Purchase #5	$137.79	12.779%	$155.3982	$155.40	$155.40	$155.40
Purchase #6	$88.42	7.849%	$95.3601	$95.36	$95.35	$95.40
Purchase #7	$59.50	3.432%	$61.542	$61.54	$61.55	$61.50
7 purchase totals =	$832.51		$919.9789	$919.98	$920.00	$919.90