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	$242.42	5.445%	$255.6198	$255.62	$255.60	$255.60
Purchase #2	$136.29	4.365%	$142.2391	$142.24	$142.25	$142.20
Purchase #3	$140.72	13.108%	$159.1656	$159.17	$159.15	$159.20
Purchase #4	$237.59	8.214%	$257.1056	$257.11	$257.10	$257.10
Purchase #5	$205.61	3.709%	$213.2361	$213.24	$213.25	$213.20
Purchase #6	$234.40	11.513%	$261.3865	$261.39	$261.40	$261.40
Purchase #7	$100.82	8.271%	$109.1588	$109.16	$109.15	$109.20
7 purchase totals =	$1,297.85		$1,397.9115	$1,397.93	$1,397.90	$1,397.90