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	$131.90	7.311%	$141.5432	$141.54	$141.55	$141.50
Purchase #2	$113.35	13.381%	$128.5174	$128.52	$128.50	$128.50
Purchase #3	$114.97	11.407%	$128.0846	$128.08	$128.10	$128.10
Purchase #4	$176.49	12.355%	$198.2953	$198.30	$198.30	$198.30
Purchase #5	$222.27	12.183%	$249.3492	$249.35	$249.35	$249.30
Purchase #6	$26.50	12.581%	$29.834	$29.83	$29.85	$29.80
Purchase #7	$117.72	12.401%	$132.3185	$132.32	$132.30	$132.30
7 purchase totals =	$903.20		$1,007.9422	$1,007.94	$1,007.95	$1,007.80