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	$250.87	11.364%	$279.3789	$279.38	$279.40	$279.40
Purchase #2	$34.46	11.642%	$38.4718	$38.47	$38.45	$38.50
Purchase #3	$227.81	4.558%	$238.1936	$238.19	$238.20	$238.20
Purchase #4	$40.92	4.817%	$42.8911	$42.89	$42.90	$42.90
Purchase #5	$220.55	3.612%	$228.5163	$228.52	$228.50	$228.50
Purchase #6	$71.48	4.534%	$74.7209	$74.72	$74.70	$74.70
Purchase #7	$165.44	10.334%	$182.5366	$182.54	$182.55	$182.50
7 purchase totals =	$1,011.53		$1,084.7092	$1,084.71	$1,084.70	$1,084.70