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	$171.52	11.797%	$191.7542	$191.75	$191.75	$191.80
Purchase #2	$179.72	10.752%	$199.0435	$199.04	$199.05	$199.00
Purchase #3	$47.73	13.830%	$54.3311	$54.33	$54.35	$54.30
Purchase #4	$156.60	6.358%	$166.5566	$166.56	$166.55	$166.60
Purchase #5	$176.25	5.768%	$186.4161	$186.42	$186.40	$186.40
Purchase #6	$23.79	3.393%	$24.5972	$24.60	$24.60	$24.60
Purchase #7	$77.71	7.607%	$83.6214	$83.62	$83.60	$83.60
7 purchase totals =	$833.32		$906.3201	$906.32	$906.30	$906.30