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	$42.42	7.272%	$45.5048	$45.50	$45.50	$45.50
Purchase #2	$250.36	12.448%	$281.5248	$281.52	$281.50	$281.50
Purchase #3	$198.86	9.506%	$217.7636	$217.76	$217.75	$217.80
Purchase #4	$44.63	5.533%	$47.0994	$47.10	$47.10	$47.10
Purchase #5	$160.51	12.451%	$180.4951	$180.50	$180.50	$180.50
Purchase #6	$111.54	6.741%	$119.0589	$119.06	$119.05	$119.10
Purchase #7	$14.32	6.550%	$15.258	$15.26	$15.25	$15.30
7 purchase totals =	$822.64		$906.7046	$906.70	$906.65	$906.80