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	$128.97	12.229%	$144.7417	$144.74	$144.75	$144.70
Purchase #2	$167.86	13.104%	$189.8564	$189.86	$189.85	$189.90
Purchase #3	$233.32	13.683%	$265.2452	$265.25	$265.25	$265.20
Purchase #4	$57.67	8.526%	$62.5869	$62.59	$62.60	$62.60
Purchase #5	$34.73	10.829%	$38.4909	$38.49	$38.50	$38.50
Purchase #6	$181.49	4.653%	$189.9347	$189.93	$189.95	$189.90
Purchase #7	$188.88	13.225%	$213.8594	$213.86	$213.85	$213.90
7 purchase totals =	$992.92		$1,104.7152	$1,104.72	$1,104.75	$1,104.70