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	$32.72	7.595%	$35.2051	$35.21	$35.20	$35.20
Purchase #2	$209.56	10.852%	$232.3015	$232.30	$232.30	$232.30
Purchase #3	$132.72	6.780%	$141.7184	$141.72	$141.70	$141.70
Purchase #4	$198.49	9.356%	$217.0607	$217.06	$217.05	$217.10
Purchase #5	$183.91	3.807%	$190.9115	$190.91	$190.90	$190.90
Purchase #6	$201.85	10.518%	$223.0806	$223.08	$223.10	$223.10
Purchase #7	$119.56	10.316%	$131.8938	$131.89	$131.90	$131.90
7 purchase totals =	$1,078.81		$1,172.1716	$1,172.17	$1,172.15	$1,172.20