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	$135.25	12.298%	$151.883	$151.88	$151.90	$151.90
Purchase #2	$142.65	12.856%	$160.9891	$160.99	$161.00	$161.00
Purchase #3	$64.99	11.585%	$72.5191	$72.52	$72.50	$72.50
Purchase #4	$108.93	9.653%	$119.445	$119.45	$119.45	$119.40
Purchase #5	$145.53	3.591%	$150.756	$150.76	$150.75	$150.80
Purchase #6	$155.85	10.240%	$171.809	$171.81	$171.80	$171.80
Purchase #7	$219.70	5.524%	$231.8362	$231.84	$231.85	$231.80
7 purchase totals =	$972.90		$1,059.2374	$1,059.25	$1,059.25	$1,059.20