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	$220.72	3.211%	$227.8073	$227.81	$227.80	$227.80
Purchase #2	$194.29	6.706%	$207.3191	$207.32	$207.30	$207.30
Purchase #3	$146.50	12.515%	$164.8345	$164.83	$164.85	$164.80
Purchase #4	$135.50	3.310%	$139.9851	$139.99	$140.00	$140.00
Purchase #5	$104.30	6.692%	$111.2798	$111.28	$111.30	$111.30
Purchase #6	$209.96	13.634%	$238.5859	$238.59	$238.60	$238.60
Purchase #7	$99.40	11.632%	$110.9622	$110.96	$110.95	$111.00
7 purchase totals =	$1,110.67		$1,200.7739	$1,200.78	$1,200.80	$1,200.80