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	$10.34	9.276%	$11.2991	$11.30	$11.30	$11.30
Purchase #2	$250.87	3.232%	$258.9781	$258.98	$259.00	$259.00
Purchase #3	$92.96	8.543%	$100.9016	$100.90	$100.90	$100.90
Purchase #4	$72.68	13.805%	$82.7135	$82.71	$82.70	$82.70
Purchase #5	$65.29	11.250%	$72.6351	$72.64	$72.65	$72.60
Purchase #6	$57.55	9.347%	$62.9292	$62.93	$62.95	$62.90
Purchase #7	$6.68	5.823%	$7.069	$7.07	$7.05	$7.10
7 purchase totals =	$556.37		$596.5256	$596.53	$596.55	$596.50