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	$104.60	11.490%	$116.6185	$116.62	$116.60	$116.60
Purchase #2	$198.83	7.385%	$213.5136	$213.51	$213.50	$213.50
Purchase #3	$52.70	5.619%	$55.6612	$55.66	$55.65	$55.70
Purchase #4	$122.33	4.480%	$127.8104	$127.81	$127.80	$127.80
Purchase #5	$133.75	12.772%	$150.8326	$150.83	$150.85	$150.80
Purchase #6	$46.97	9.798%	$51.5721	$51.57	$51.55	$51.60
Purchase #7	$71.41	6.310%	$75.916	$75.92	$75.90	$75.90
7 purchase totals =	$730.59		$791.9244	$791.92	$791.85	$791.90