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	$38.85	3.385%	$40.1651	$40.17	$40.15	$40.20
Purchase #2	$124.36	11.734%	$138.9524	$138.95	$138.95	$139.00
Purchase #3	$72.89	8.195%	$78.8633	$78.86	$78.85	$78.90
Purchase #4	$232.66	13.865%	$264.9183	$264.92	$264.90	$264.90
Purchase #5	$27.71	5.245%	$29.1634	$29.16	$29.15	$29.20
Purchase #6	$165.92	12.519%	$186.6915	$186.69	$186.70	$186.70
Purchase #7	$168.72	3.813%	$175.1533	$175.15	$175.15	$175.20
7 purchase totals =	$831.11		$913.9073	$913.90	$913.85	$914.10