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	$76.46	3.109%	$78.8371	$78.84	$78.85	$78.80
Purchase #2	$74.84	9.261%	$81.7709	$81.77	$81.75	$81.80
Purchase #3	$145.36	9.263%	$158.8247	$158.82	$158.80	$158.80
Purchase #4	$69.53	12.433%	$78.1747	$78.17	$78.15	$78.20
Purchase #5	$205.91	11.136%	$228.8401	$228.84	$228.85	$228.80
Purchase #6	$179.67	10.836%	$199.139	$199.14	$199.15	$199.10
Purchase #7	$72.79	4.263%	$75.893	$75.89	$75.90	$75.90
7 purchase totals =	$824.56		$901.4795	$901.47	$901.45	$901.40