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	$126.93	9.541%	$139.0404	$139.04	$139.05	$139.00
Purchase #2	$78.60	11.185%	$87.3914	$87.39	$87.40	$87.40
Purchase #3	$45.68	13.425%	$51.8125	$51.81	$51.80	$51.80
Purchase #4	$241.58	11.368%	$269.0428	$269.04	$269.05	$269.00
Purchase #5	$87.92	5.125%	$92.4259	$92.43	$92.45	$92.40
Purchase #6	$73.79	5.860%	$78.1141	$78.11	$78.10	$78.10
Purchase #7	$76.54	3.192%	$78.9832	$78.98	$79.00	$79.00
7 purchase totals =	$731.04		$796.8103	$796.80	$796.85	$796.70