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	$143.55	8.309%	$155.4776	$155.48	$155.50	$155.50
Purchase #2	$155.28	9.861%	$170.5922	$170.59	$170.60	$170.60
Purchase #3	$201.50	12.198%	$226.079	$226.08	$226.10	$226.10
Purchase #4	$134.35	4.115%	$139.8785	$139.88	$139.90	$139.90
Purchase #5	$231.89	11.404%	$258.3347	$258.33	$258.35	$258.30
Purchase #6	$61.48	6.517%	$65.4867	$65.49	$65.50	$65.50
Purchase #7	$29.28	6.577%	$31.2057	$31.21	$31.20	$31.20
7 purchase totals =	$957.33		$1,047.0544	$1,047.06	$1,047.15	$1,047.10