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	$45.47	12.761%	$51.2724	$51.27	$51.25	$51.30
Purchase #2	$92.31	12.869%	$104.1894	$104.19	$104.20	$104.20
Purchase #3	$117.89	4.544%	$123.2469	$123.25	$123.25	$123.20
Purchase #4	$173.46	11.534%	$193.4669	$193.47	$193.45	$193.50
Purchase #5	$40.57	6.471%	$43.1953	$43.20	$43.20	$43.20
Purchase #6	$89.28	8.366%	$96.7492	$96.75	$96.75	$96.70
Purchase #7	$126.29	10.437%	$139.4709	$139.47	$139.45	$139.50
7 purchase totals =	$685.27		$751.5910	$751.60	$751.55	$751.60