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	$127.81	7.826%	$137.8124	$137.81	$137.80	$137.80
Purchase #2	$76.88	7.472%	$82.6245	$82.62	$82.60	$82.60
Purchase #3	$175.44	4.550%	$183.4225	$183.42	$183.40	$183.40
Purchase #4	$170.41	13.508%	$193.429	$193.43	$193.45	$193.40
Purchase #5	$246.50	12.745%	$277.9164	$277.92	$277.90	$277.90
Purchase #6	$155.48	8.403%	$168.545	$168.55	$168.55	$168.50
Purchase #7	$35.33	6.798%	$37.7317	$37.73	$37.75	$37.70
7 purchase totals =	$987.85		$1,081.4815	$1,081.48	$1,081.45	$1,081.30