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	$141.71	4.809%	$148.5248	$148.52	$148.50	$148.50
Purchase #2	$165.57	13.432%	$187.8094	$187.81	$187.80	$187.80
Purchase #3	$131.29	4.634%	$137.374	$137.37	$137.35	$137.40
Purchase #4	$103.83	3.524%	$107.489	$107.49	$107.50	$107.50
Purchase #5	$132.45	9.604%	$145.1705	$145.17	$145.15	$145.20
Purchase #6	$98.47	13.441%	$111.7054	$111.71	$111.70	$111.70
Purchase #7	$128.34	8.546%	$139.3079	$139.31	$139.30	$139.30
7 purchase totals =	$901.66		$977.3810	$977.38	$977.30	$977.40