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	$89.42	12.296%	$100.4151	$100.42	$100.40	$100.40
Purchase #2	$76.27	5.214%	$80.2467	$80.25	$80.25	$80.20
Purchase #3	$176.45	8.538%	$191.5153	$191.52	$191.50	$191.50
Purchase #4	$184.80	10.790%	$204.7399	$204.74	$204.75	$204.70
Purchase #5	$63.49	3.441%	$65.6747	$65.67	$65.65	$65.70
Purchase #6	$82.72	6.829%	$88.3689	$88.37	$88.35	$88.40
Purchase #7	$206.77	4.145%	$215.3406	$215.34	$215.35	$215.30
7 purchase totals =	$879.92		$946.3012	$946.31	$946.25	$946.20