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	$23.78	3.141%	$24.5269	$24.53	$24.55	$24.50
Purchase #2	$118.80	7.456%	$127.6577	$127.66	$127.65	$127.70
Purchase #3	$38.81	8.860%	$42.2486	$42.25	$42.25	$42.20
Purchase #4	$177.36	6.176%	$188.3138	$188.31	$188.30	$188.30
Purchase #5	$29.85	12.556%	$33.598	$33.60	$33.60	$33.60
Purchase #6	$47.64	6.398%	$50.688	$50.69	$50.70	$50.70
Purchase #7	$232.82	6.656%	$248.3165	$248.32	$248.30	$248.30
7 purchase totals =	$669.06		$715.3495	$715.36	$715.35	$715.30