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	$123.88	12.108%	$138.8794	$138.88	$138.90	$138.90
Purchase #2	$139.50	13.531%	$158.3757	$158.38	$158.40	$158.40
Purchase #3	$174.61	9.691%	$191.5315	$191.53	$191.55	$191.50
Purchase #4	$99.39	4.527%	$103.8894	$103.89	$103.90	$103.90
Purchase #5	$28.52	4.777%	$29.8824	$29.88	$29.90	$29.90
Purchase #6	$232.72	4.384%	$242.9224	$242.92	$242.90	$242.90
Purchase #7	$180.44	3.814%	$187.322	$187.32	$187.30	$187.30
7 purchase totals =	$979.06		$1,052.8028	$1,052.80	$1,052.85	$1,052.80