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	$172.94	6.283%	$183.8058	$183.81	$183.80	$183.80
Purchase #2	$232.93	10.369%	$257.0825	$257.08	$257.10	$257.10
Purchase #3	$212.73	4.459%	$222.2156	$222.22	$222.20	$222.20
Purchase #4	$126.53	12.277%	$142.0641	$142.06	$142.05	$142.10
Purchase #5	$67.47	7.509%	$72.5363	$72.54	$72.55	$72.50
Purchase #6	$176.25	12.248%	$197.8371	$197.84	$197.85	$197.80
Purchase #7	$183.69	7.202%	$196.9194	$196.92	$196.90	$196.90
7 purchase totals =	$1,172.54		$1,272.4608	$1,272.47	$1,272.45	$1,272.40