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	$88.28	13.630%	$100.3126	$100.31	$100.30	$100.30
Purchase #2	$203.54	8.536%	$220.9142	$220.91	$220.90	$220.90
Purchase #3	$77.60	4.761%	$81.2945	$81.29	$81.30	$81.30
Purchase #4	$78.39	3.266%	$80.9502	$80.95	$80.95	$81.00
Purchase #5	$248.74	7.272%	$266.8284	$266.83	$266.85	$266.80
Purchase #6	$188.48	6.175%	$200.1186	$200.12	$200.10	$200.10
Purchase #7	$85.95	5.742%	$90.8852	$90.89	$90.90	$90.90
7 purchase totals =	$970.98		$1,041.3037	$1,041.30	$1,041.30	$1,041.30