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	$163.39	7.188%	$175.1345	$175.13	$175.15	$175.10
Purchase #2	$91.45	9.656%	$100.2804	$100.28	$100.30	$100.30
Purchase #3	$109.79	12.315%	$123.3106	$123.31	$123.30	$123.30
Purchase #4	$115.59	10.696%	$127.9535	$127.95	$127.95	$128.00
Purchase #5	$22.76	12.235%	$25.5447	$25.54	$25.55	$25.50
Purchase #6	$167.58	12.694%	$188.8526	$188.85	$188.85	$188.90
Purchase #7	$209.28	8.105%	$226.2421	$226.24	$226.25	$226.20
7 purchase totals =	$879.84		$967.3184	$967.30	$967.35	$967.30