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	$250.26	10.836%	$277.3782	$277.38	$277.40	$277.40
Purchase #2	$54.96	8.425%	$59.5904	$59.59	$59.60	$59.60
Purchase #3	$238.38	6.658%	$254.2513	$254.25	$254.25	$254.30
Purchase #4	$87.57	13.706%	$99.5723	$99.57	$99.55	$99.60
Purchase #5	$119.52	12.499%	$134.4588	$134.46	$134.45	$134.50
Purchase #6	$61.50	9.114%	$67.1051	$67.11	$67.10	$67.10
Purchase #7	$181.73	6.208%	$193.0118	$193.01	$193.00	$193.00
7 purchase totals =	$993.92		$1,085.3679	$1,085.37	$1,085.35	$1,085.50