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	$28.72	11.188%	$31.9332	$31.93	$31.95	$31.90
Purchase #2	$51.66	11.324%	$57.51	$57.51	$57.50	$57.50
Purchase #3	$108.91	9.453%	$119.2053	$119.21	$119.20	$119.20
Purchase #4	$174.50	3.334%	$180.3178	$180.32	$180.30	$180.30
Purchase #5	$233.85	3.559%	$242.1727	$242.17	$242.15	$242.20
Purchase #6	$137.49	10.683%	$152.1781	$152.18	$152.20	$152.20
Purchase #7	$45.27	11.503%	$50.4774	$50.48	$50.50	$50.50
7 purchase totals =	$780.40		$833.7945	$833.80	$833.80	$833.80