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	$28.62	9.824%	$31.4316	$31.43	$31.45	$31.40
Purchase #2	$237.60	4.831%	$249.0785	$249.08	$249.10	$249.10
Purchase #3	$101.63	4.523%	$106.2267	$106.23	$106.25	$106.20
Purchase #4	$66.85	6.808%	$71.4011	$71.40	$71.40	$71.40
Purchase #5	$25.96	10.190%	$28.6053	$28.61	$28.60	$28.60
Purchase #6	$29.67	7.781%	$31.9786	$31.98	$32.00	$32.00
Purchase #7	$93.35	7.729%	$100.565	$100.57	$100.55	$100.60
7 purchase totals =	$583.68		$619.2868	$619.30	$619.35	$619.30