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	$38.56	10.422%	$42.5787	$42.58	$42.60	$42.60
Purchase #2	$19.34	5.246%	$20.3546	$20.35	$20.35	$20.40
Purchase #3	$43.66	9.674%	$47.8837	$47.88	$47.90	$47.90
Purchase #4	$16.54	9.477%	$18.1075	$18.11	$18.10	$18.10
Purchase #5	$105.37	5.339%	$110.9957	$111.00	$111.00	$111.00
Purchase #6	$104.30	13.289%	$118.1604	$118.16	$118.15	$118.20
Purchase #7	$174.87	6.659%	$186.5146	$186.51	$186.50	$186.50
7 purchase totals =	$502.64		$544.5952	$544.59	$544.60	$544.70