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	$80.85	12.857%	$91.2449	$91.24	$91.25	$91.20
Purchase #2	$172.76	13.634%	$196.3141	$196.31	$196.30	$196.30
Purchase #3	$100.55	4.223%	$104.7962	$104.80	$104.80	$104.80
Purchase #4	$208.48	6.767%	$222.5878	$222.59	$222.60	$222.60
Purchase #5	$247.65	10.600%	$273.9009	$273.90	$273.90	$273.90
Purchase #6	$196.80	7.515%	$211.5895	$211.59	$211.60	$211.60
Purchase #7	$127.79	9.269%	$139.6349	$139.63	$139.65	$139.60
7 purchase totals =	$1,134.88		$1,240.0683	$1,240.06	$1,240.10	$1,240.00