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	$47.93	12.604%	$53.9711	$53.97	$53.95	$54.00
Purchase #2	$216.70	4.805%	$227.1124	$227.11	$227.10	$227.10
Purchase #3	$90.60	3.575%	$93.839	$93.84	$93.85	$93.80
Purchase #4	$94.78	11.393%	$105.5783	$105.58	$105.60	$105.60
Purchase #5	$81.42	10.705%	$90.136	$90.14	$90.15	$90.10
Purchase #6	$74.60	11.735%	$83.3543	$83.35	$83.35	$83.40
Purchase #7	$237.44	3.867%	$246.6218	$246.62	$246.60	$246.60
7 purchase totals =	$843.47		$900.6129	$900.61	$900.60	$900.60