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	$80.39	11.384%	$89.5416	$89.54	$89.55	$89.50
Purchase #2	$71.79	13.367%	$81.3862	$81.39	$81.40	$81.40
Purchase #3	$162.83	8.650%	$176.9148	$176.91	$176.90	$176.90
Purchase #4	$118.55	4.248%	$123.586	$123.59	$123.60	$123.60
Purchase #5	$133.38	6.531%	$142.091	$142.09	$142.10	$142.10
Purchase #6	$83.67	4.443%	$87.3875	$87.39	$87.40	$87.40
Purchase #7	$45.67	10.276%	$50.363	$50.36	$50.35	$50.40
7 purchase totals =	$696.28		$751.2701	$751.27	$751.30	$751.30