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	$231.41	13.659%	$263.0183	$263.02	$263.00	$263.00
Purchase #2	$98.49	3.588%	$102.0238	$102.02	$102.00	$102.00
Purchase #3	$54.99	6.284%	$58.4456	$58.45	$58.45	$58.40
Purchase #4	$12.54	12.169%	$14.066	$14.07	$14.05	$14.10
Purchase #5	$189.78	12.667%	$213.8194	$213.82	$213.80	$213.80
Purchase #6	$123.33	3.352%	$127.464	$127.46	$127.45	$127.50
Purchase #7	$37.37	12.668%	$42.104	$42.10	$42.10	$42.10
7 purchase totals =	$747.91		$820.9411	$820.94	$820.85	$820.90