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	$209.30	13.175%	$236.8753	$236.88	$236.90	$236.90
Purchase #2	$49.91	9.327%	$54.5651	$54.57	$54.55	$54.60
Purchase #3	$198.91	7.864%	$214.5523	$214.55	$214.55	$214.60
Purchase #4	$80.75	6.180%	$85.7404	$85.74	$85.75	$85.70
Purchase #5	$161.66	3.165%	$166.7765	$166.78	$166.80	$166.80
Purchase #6	$31.58	13.434%	$35.8225	$35.82	$35.80	$35.80
Purchase #7	$69.45	13.180%	$78.6035	$78.60	$78.60	$78.60
7 purchase totals =	$801.56		$872.9356	$872.94	$872.95	$873.00