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	$30.30	8.479%	$32.8691	$32.87	$32.85	$32.90
Purchase #2	$234.59	7.870%	$253.0522	$253.05	$253.05	$253.10
Purchase #3	$63.86	12.222%	$71.665	$71.67	$71.65	$71.70
Purchase #4	$213.38	12.280%	$239.5831	$239.58	$239.60	$239.60
Purchase #5	$149.97	9.627%	$164.4076	$164.41	$164.40	$164.40
Purchase #6	$17.31	5.680%	$18.2932	$18.29	$18.30	$18.30
Purchase #7	$90.64	13.610%	$102.9761	$102.98	$103.00	$103.00
7 purchase totals =	$800.05		$882.8463	$882.85	$882.85	$883.00