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	$143.46	7.840%	$154.7073	$154.71	$154.70	$154.70
Purchase #2	$51.47	12.484%	$57.8955	$57.90	$57.90	$57.90
Purchase #3	$43.94	4.227%	$45.7973	$45.80	$45.80	$45.80
Purchase #4	$172.27	9.205%	$188.1275	$188.13	$188.15	$188.10
Purchase #5	$117.30	7.780%	$126.4259	$126.43	$126.45	$126.40
Purchase #6	$125.46	12.289%	$140.8778	$140.88	$140.90	$140.90
Purchase #7	$61.51	8.192%	$66.5489	$66.55	$66.55	$66.50
7 purchase totals =	$715.41		$780.3802	$780.40	$780.45	$780.30