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	$30.60	12.675%	$34.4786	$34.48	$34.50	$34.50
Purchase #2	$175.61	7.842%	$189.3813	$189.38	$189.40	$189.40
Purchase #3	$163.50	11.493%	$182.2911	$182.29	$182.30	$182.30
Purchase #4	$124.26	3.493%	$128.6004	$128.60	$128.60	$128.60
Purchase #5	$170.67	4.734%	$178.7495	$178.75	$178.75	$178.70
Purchase #6	$213.51	4.400%	$222.9044	$222.90	$222.90	$222.90
Purchase #7	$78.25	4.413%	$81.7032	$81.70	$81.70	$81.70
7 purchase totals =	$956.40		$1,018.1085	$1,018.10	$1,018.15	$1,018.10