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	$31.90	7.152%	$34.1815	$34.18	$34.20	$34.20
Purchase #2	$85.40	5.176%	$89.8203	$89.82	$89.80	$89.80
Purchase #3	$64.74	9.499%	$70.8897	$70.89	$70.90	$70.90
Purchase #4	$82.80	4.400%	$86.4432	$86.44	$86.45	$86.40
Purchase #5	$140.78	12.397%	$158.2325	$158.23	$158.25	$158.20
Purchase #6	$66.97	11.797%	$74.8705	$74.87	$74.85	$74.90
Purchase #7	$87.29	9.163%	$95.2884	$95.29	$95.30	$95.30
7 purchase totals =	$559.88		$609.7261	$609.72	$609.75	$609.70