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	$44.37	12.413%	$49.8776	$49.88	$49.90	$49.90
Purchase #2	$216.48	10.119%	$238.3856	$238.39	$238.40	$238.40
Purchase #3	$215.76	6.233%	$229.2083	$229.21	$229.20	$229.20
Purchase #4	$85.86	3.555%	$88.9123	$88.91	$88.90	$88.90
Purchase #5	$83.49	7.243%	$89.5372	$89.54	$89.55	$89.50
Purchase #6	$190.34	4.573%	$199.0442	$199.04	$199.05	$199.00
Purchase #7	$149.78	3.203%	$154.5775	$154.58	$154.60	$154.60
7 purchase totals =	$986.08		$1,049.5427	$1,049.55	$1,049.60	$1,049.50