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	$18.89	7.158%	$20.2421	$20.24	$20.25	$20.20
Purchase #2	$129.53	10.502%	$143.1332	$143.13	$143.15	$143.10
Purchase #3	$100.89	13.765%	$114.7775	$114.78	$114.80	$114.80
Purchase #4	$103.91	9.405%	$113.6827	$113.68	$113.70	$113.70
Purchase #5	$248.90	7.240%	$266.9204	$266.92	$266.90	$266.90
Purchase #6	$137.72	13.638%	$156.5023	$156.50	$156.50	$156.50
Purchase #7	$223.57	12.137%	$250.7047	$250.70	$250.70	$250.70
7 purchase totals =	$963.41		$1,065.9629	$1,065.95	$1,066.00	$1,065.90