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	$37.70	12.669%	$42.4762	$42.48	$42.50	$42.50
Purchase #2	$210.25	4.682%	$220.0939	$220.09	$220.10	$220.10
Purchase #3	$192.40	9.323%	$210.3375	$210.34	$210.35	$210.30
Purchase #4	$213.51	7.497%	$229.5168	$229.52	$229.50	$229.50
Purchase #5	$6.74	4.720%	$7.0581	$7.06	$7.05	$7.10
Purchase #6	$38.43	4.721%	$40.2443	$40.24	$40.25	$40.20
Purchase #7	$196.39	12.658%	$221.249	$221.25	$221.25	$221.20
7 purchase totals =	$895.42		$970.9758	$970.98	$971.00	$970.90