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	$67.27	13.446%	$76.3151	$76.32	$76.30	$76.30
Purchase #2	$234.84	8.710%	$255.2946	$255.29	$255.30	$255.30
Purchase #3	$160.30	9.401%	$175.3698	$175.37	$175.35	$175.40
Purchase #4	$48.60	10.658%	$53.7798	$53.78	$53.80	$53.80
Purchase #5	$107.76	4.841%	$112.9767	$112.98	$113.00	$113.00
Purchase #6	$150.64	4.846%	$157.94	$157.94	$157.95	$157.90
Purchase #7	$137.89	6.825%	$147.301	$147.30	$147.30	$147.30
7 purchase totals =	$907.30		$978.9770	$978.98	$979.00	$979.00