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	$75.80	9.103%	$82.7001	$82.70	$82.70	$82.70
Purchase #2	$76.67	5.517%	$80.8999	$80.90	$80.90	$80.90
Purchase #3	$171.54	5.742%	$181.3898	$181.39	$181.40	$181.40
Purchase #4	$200.74	6.513%	$213.8142	$213.81	$213.80	$213.80
Purchase #5	$64.60	11.367%	$71.9431	$71.94	$71.95	$71.90
Purchase #6	$238.74	5.196%	$251.1449	$251.14	$251.15	$251.10
Purchase #7	$118.93	12.262%	$133.5132	$133.51	$133.50	$133.50
7 purchase totals =	$947.02		$1,015.4052	$1,015.39	$1,015.40	$1,015.30