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	$249.96	8.329%	$270.7792	$270.78	$270.80	$270.80
Purchase #2	$213.65	4.142%	$222.4994	$222.50	$222.50	$222.50
Purchase #3	$69.57	12.853%	$78.5118	$78.51	$78.50	$78.50
Purchase #4	$23.67	5.284%	$24.9207	$24.92	$24.90	$24.90
Purchase #5	$147.60	5.615%	$155.8877	$155.89	$155.90	$155.90
Purchase #6	$161.78	6.190%	$171.7942	$171.79	$171.80	$171.80
Purchase #7	$203.78	6.657%	$217.3456	$217.35	$217.35	$217.30
7 purchase totals =	$1,070.01		$1,141.7386	$1,141.74	$1,141.75	$1,141.70