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	$143.72	13.326%	$162.8721	$162.87	$162.85	$162.90
Purchase #2	$73.98	12.714%	$83.3858	$83.39	$83.40	$83.40
Purchase #3	$10.70	11.424%	$11.9224	$11.92	$11.90	$11.90
Purchase #4	$77.46	6.856%	$82.7707	$82.77	$82.75	$82.80
Purchase #5	$132.87	9.637%	$145.6747	$145.67	$145.65	$145.70
Purchase #6	$205.79	6.312%	$218.7795	$218.78	$218.80	$218.80
Purchase #7	$205.84	9.542%	$225.4813	$225.48	$225.50	$225.50
7 purchase totals =	$850.36		$930.8865	$930.88	$930.85	$931.00