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	$117.25	10.524%	$129.5894	$129.59	$129.60	$129.60
Purchase #2	$185.42	7.742%	$199.7752	$199.78	$199.80	$199.80
Purchase #3	$104.34	5.147%	$109.7104	$109.71	$109.70	$109.70
Purchase #4	$187.42	5.750%	$198.1967	$198.20	$198.20	$198.20
Purchase #5	$167.70	12.376%	$188.4546	$188.45	$188.45	$188.50
Purchase #6	$129.77	12.131%	$145.5124	$145.51	$145.50	$145.50
Purchase #7	$154.74	10.592%	$171.1301	$171.13	$171.15	$171.10
7 purchase totals =	$1,046.64		$1,142.3688	$1,142.37	$1,142.40	$1,142.40