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	$189.69	10.451%	$209.5145	$209.51	$209.50	$209.50
Purchase #2	$61.87	5.718%	$65.4077	$65.41	$65.40	$65.40
Purchase #3	$241.39	4.503%	$252.2598	$252.26	$252.25	$252.30
Purchase #4	$203.50	8.815%	$221.4385	$221.44	$221.45	$221.40
Purchase #5	$80.52	10.627%	$89.0769	$89.08	$89.10	$89.10
Purchase #6	$78.48	10.544%	$86.7549	$86.75	$86.75	$86.80
Purchase #7	$28.71	9.436%	$31.4191	$31.42	$31.40	$31.40
7 purchase totals =	$884.16		$955.8714	$955.87	$955.85	$955.90