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	$78.42	6.656%	$83.6396	$83.64	$83.65	$83.60
Purchase #2	$73.40	12.398%	$82.5001	$82.50	$82.50	$82.50
Purchase #3	$172.55	12.750%	$194.5501	$194.55	$194.55	$194.60
Purchase #4	$132.33	4.519%	$138.31	$138.31	$138.30	$138.30
Purchase #5	$100.50	13.813%	$114.3821	$114.38	$114.40	$114.40
Purchase #6	$32.42	4.395%	$33.8449	$33.84	$33.85	$33.80
Purchase #7	$180.87	13.692%	$205.6347	$205.63	$205.65	$205.60
7 purchase totals =	$770.49		$852.8615	$852.85	$852.90	$852.80