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	$54.90	4.330%	$57.2772	$57.28	$57.30	$57.30
Purchase #2	$26.48	11.317%	$29.4767	$29.48	$29.50	$29.50
Purchase #3	$85.88	7.281%	$92.1329	$92.13	$92.15	$92.10
Purchase #4	$54.43	9.704%	$59.7119	$59.71	$59.70	$59.70
Purchase #5	$34.37	10.864%	$38.104	$38.10	$38.10	$38.10
Purchase #6	$119.93	9.622%	$131.4697	$131.47	$131.45	$131.50
Purchase #7	$21.65	11.587%	$24.1586	$24.16	$24.15	$24.20
7 purchase totals =	$397.64		$432.3310	$432.33	$432.35	$432.40