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	$245.94	8.147%	$265.9767	$265.98	$266.00	$266.00
Purchase #2	$39.85	5.148%	$41.9015	$41.90	$41.90	$41.90
Purchase #3	$166.68	4.238%	$173.7439	$173.74	$173.75	$173.70
Purchase #4	$156.74	6.748%	$167.3168	$167.32	$167.30	$167.30
Purchase #5	$194.44	8.797%	$211.5449	$211.54	$211.55	$211.50
Purchase #6	$53.63	10.606%	$59.318	$59.32	$59.30	$59.30
Purchase #7	$33.60	12.231%	$37.7096	$37.71	$37.70	$37.70
7 purchase totals =	$890.88		$957.5114	$957.51	$957.50	$957.40