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	$68.81	5.596%	$72.6606	$72.66	$72.65	$72.70
Purchase #2	$249.84	4.109%	$260.1059	$260.11	$260.10	$260.10
Purchase #3	$42.39	8.121%	$45.8325	$45.83	$45.85	$45.80
Purchase #4	$105.38	10.844%	$116.8074	$116.81	$116.80	$116.80
Purchase #5	$228.85	4.425%	$238.9766	$238.98	$239.00	$239.00
Purchase #6	$178.67	13.541%	$202.8637	$202.86	$202.85	$202.90
Purchase #7	$36.70	11.345%	$40.8636	$40.86	$40.85	$40.90
7 purchase totals =	$910.64		$978.1103	$978.11	$978.10	$978.20