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	$26.27	8.322%	$28.4562	$28.46	$28.45	$28.50
Purchase #2	$141.57	12.285%	$158.9619	$158.96	$158.95	$159.00
Purchase #3	$56.54	10.260%	$62.341	$62.34	$62.35	$62.30
Purchase #4	$217.64	3.599%	$225.4729	$225.47	$225.45	$225.50
Purchase #5	$86.59	3.262%	$89.4146	$89.41	$89.40	$89.40
Purchase #6	$201.83	6.153%	$214.2486	$214.25	$214.25	$214.20
Purchase #7	$177.56	4.437%	$185.4383	$185.44	$185.45	$185.40
7 purchase totals =	$908.00		$964.3335	$964.33	$964.30	$964.30