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	$110.37	11.777%	$123.3683	$123.37	$123.35	$123.40
Purchase #2	$165.67	10.169%	$182.517	$182.52	$182.50	$182.50
Purchase #3	$179.99	9.159%	$196.4753	$196.48	$196.50	$196.50
Purchase #4	$61.69	5.433%	$65.0416	$65.04	$65.05	$65.00
Purchase #5	$197.43	9.820%	$216.8176	$216.82	$216.80	$216.80
Purchase #6	$138.48	11.627%	$154.5811	$154.58	$154.60	$154.60
Purchase #7	$117.65	7.561%	$126.5455	$126.55	$126.55	$126.50
7 purchase totals =	$971.28		$1,065.3464	$1,065.36	$1,065.35	$1,065.30