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	$73.60	8.840%	$80.1062	$80.11	$80.10	$80.10
Purchase #2	$227.74	12.371%	$255.9137	$255.91	$255.90	$255.90
Purchase #3	$188.39	3.329%	$194.6615	$194.66	$194.65	$194.70
Purchase #4	$78.83	6.384%	$83.8625	$83.86	$83.85	$83.90
Purchase #5	$33.54	7.144%	$35.9361	$35.94	$35.95	$35.90
Purchase #6	$166.88	10.869%	$185.0182	$185.02	$185.00	$185.00
Purchase #7	$146.93	8.565%	$159.5146	$159.51	$159.50	$159.50
7 purchase totals =	$915.91		$995.0128	$995.01	$994.95	$995.00