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	$232.77	10.608%	$257.4622	$257.46	$257.45	$257.50
Purchase #2	$16.74	10.827%	$18.5524	$18.55	$18.55	$18.60
Purchase #3	$168.86	6.654%	$180.0959	$180.10	$180.10	$180.10
Purchase #4	$222.94	11.721%	$249.0708	$249.07	$249.05	$249.10
Purchase #5	$233.40	10.633%	$258.2174	$258.22	$258.20	$258.20
Purchase #6	$141.59	7.430%	$152.1101	$152.11	$152.10	$152.10
Purchase #7	$168.41	9.754%	$184.8367	$184.84	$184.85	$184.80
7 purchase totals =	$1,184.71		$1,300.3455	$1,300.35	$1,300.30	$1,300.40