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	$18.55	8.855%	$20.1926	$20.19	$20.20	$20.20
Purchase #2	$117.94	8.726%	$128.2314	$128.23	$128.25	$128.20
Purchase #3	$33.99	11.684%	$37.9614	$37.96	$37.95	$38.00
Purchase #4	$8.25	6.836%	$8.814	$8.81	$8.80	$8.80
Purchase #5	$56.66	5.820%	$59.9576	$59.96	$59.95	$60.00
Purchase #6	$94.83	7.695%	$102.1272	$102.13	$102.15	$102.10
Purchase #7	$250.60	11.578%	$279.6145	$279.61	$279.60	$279.60
7 purchase totals =	$580.82		$636.8987	$636.89	$636.90	$636.90