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	$30.89	13.183%	$34.9622	$34.96	$34.95	$35.00
Purchase #2	$92.38	5.513%	$97.4729	$97.47	$97.45	$97.50
Purchase #3	$200.74	10.823%	$222.4661	$222.47	$222.45	$222.50
Purchase #4	$204.25	6.357%	$217.2342	$217.23	$217.25	$217.20
Purchase #5	$28.86	6.420%	$30.7128	$30.71	$30.70	$30.70
Purchase #6	$185.85	8.118%	$200.9373	$200.94	$200.95	$200.90
Purchase #7	$187.82	6.152%	$199.3747	$199.37	$199.35	$199.40
7 purchase totals =	$930.79		$1,003.1602	$1,003.15	$1,003.10	$1,003.20